Waveguides with embedded components to improve intensity distributions

ABSTRACT

An apparatus for use in replicating an image associated with an input-pupil to an output-pupil includes a planar optical waveguide including a bulk-substrate, and also including an input-coupler, an intermediate-component and an output-coupler. The input-coupler couples light corresponding to the image into the bulk-substrate and towards the intermediate-component. The intermediate-component performs horizontal or vertical pupil expansion and directs the light corresponding to the image towards the output-coupler. The output-coupler performs the other one of horizontal or vertical pupil expansion and couples light corresponding to the image, which travels from the input-coupler to the output-coupler, out of the waveguide. The apparatus further includes a volume layer, embedded between first and second major planar surfaces of the bulk-substrate, configured to cause light that is output by the output-coupler to have a more uniform intensity distribution compared to if the volume layer were absent.

BACKGROUND

Various types of computing, entertainment, and/or mobile devices can beimplemented with a transparent or semi-transparent display through whicha user of a device can view the surrounding environment. Such devices,which can be referred to as see-through, mixed reality display devicesystems, or as augmented reality (AR) systems, enable a user to seethrough the transparent or semi-transparent display of a device to viewthe surrounding environment, and also see images of virtual objects(e.g., text, graphics, video, etc.) that are generated for display toappear as a part of, and/or overlaid upon, the surrounding environment.These devices, which can be implemented as head-mounted display (HMD)glasses or other wearable display devices, but are not limited thereto,often utilize optical waveguides to replicate an image, e.g., producedby a display engine, to a location where a user of a device can view theimage as a virtual image in an augmented reality environment. As this isstill an emerging technology, there are certain challenges associatedwith utilizing waveguides to display images of virtual objects to auser.

SUMMARY

Certain embodiments described herein relate to an apparatus for use inreplicating an image associated with an input-pupil to an output-pupil.The apparatus includes a planar optical waveguide including abulk-substrate, and also includes an input-coupler, anintermediate-component and an output-coupler. The input-coupler coupleslight corresponding to the image into the bulk-substrate and towards theintermediate-component. The intermediate-component performs horizontalor vertical pupil expansion and directs the light corresponding to theimage towards the output-coupler. The output-coupler performs the otherone of horizontal or vertical pupil expansion and couples lightcorresponding to the image, which travels from the input-coupler to theoutput-coupler, out of the waveguide. In certain embodiments, theintermediate-component can be eliminated, in which case theinput-coupler directs light coupled into the bulk-substrate towards theoutput-coupler. In certain embodiments, the apparatus further includes avolume layer, embedded between opposing major planar surfaces of thebulk-substrate, to cause light that is output by the output-coupler tohave a more uniform intensity distribution compared to if the volumelayer were absent. The volume layer, in certain embodiments, is aswitchable liquid crystal (LC) layer. The volume layer, in otherembodiments, includes one or more volume Bragg gratings (VBGs), each ofwhich forms a part of a hybrid grating that includes both a surfacerelief grating (SRG) and a VBG.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are front, top and side views, respectively, of anexemplary waveguide that can be used to replicate an image associatedwith an input-pupil to an expanded output-pupil.

FIG. 2 is side view of the exemplary waveguide introduced with referenceto FIGS. 1A, 1B and 1C, and also shows a display engine that generatesan image including angular content that is coupled into the waveguide byan input-coupler, and also shows an eye that is viewing the image withinan eye box that is proximate the output-coupler.

FIG. 3, which is similar to FIG. 1A because it provides a front view ofthe waveguide, is used to explain how light that is coupled into thewaveguide by an input-coupler, travels by way of total internalreflection (TIR) from the input-coupler to an intermediate-component,and by way of TIR from the intermediate-component to an output-coupler,where it exits the waveguide.

FIG. 4 conceptually illustrates how the intermediate-component of theexemplary waveguide, introduced in the earlier FIGS., can causemultiple-loop interference.

FIG. 5A is used to conceptually illustrate how a pupil is replicatedwithin a waveguide. FIG. 5B illustrates an exemplary pupil distributionalong the line B-B shown in FIG. 5A. FIG. 5C illustrates an alternativepupil distribution, corresponding to a situation where there is no pupiloverlap between pupils replicated within a waveguide. FIG. 5Dillustrates a substantially uniform pupil distribution.

FIG. 6 is used to illustrate non-uniformities in local and globalintensities which may occur when performing imaging, and morespecifically pupil replication, using an optical waveguide.

FIG. 7 is a top view of a waveguide that that utilizes a liquid crystalpolymer (LCP) coating to improve the uniformity in the intensity oflight that exits the waveguide, in accordance with certain embodimentsof the present technology.

FIG. 8 is a top view of a waveguide that utilizes materials havingmismatched indexes of refraction to improve the uniformity in theintensity of light that exits the waveguide, in accordance with certainembodiments of the present technology.

FIGS. 9A and 9B are, respectively, top and side views of a waveguidethat includes double-side diffractive optical elements (DOEs) to improvethe uniformity in the intensity of light that exits the waveguide, inaccordance with certain embodiments of the present technology.

FIG. 10 is a top view of a waveguide that includes a switchable liquidcrystal (LC) layer embedded in the waveguide to improve the uniformityin the intensity of light that exits the waveguide, in accordance withcertain embodiments of the present technology.

FIG. 11 is a top view of a waveguide that includes hybrid gratings, eachof which is a hybrid of a surface relief grating (SRG) and acorresponding volume Bragg grating (VBG), which are used to improve theuniformity in the intensity of light that exits the waveguide, inaccordance with certain embodiments of the present technology.

FIG. 12 illustrates exemplary k-vectors and corresponding exemplaryK-vector angels of a diffraction grating of an input-coupler of awaveguide.

DETAILED DESCRIPTION

Certain embodiments of the present technology relate to apparatuses foruse in replicating an image associated with an input-pupil to anoutput-pupil. Such apparatuses can include a waveguide. As will bediscussed in further details below, where waveguides are used to performpupil replication (also referred to as image replication),non-uniformities in local and global intensities may occur, which mayresult in dark and light fringes and dark blotches when the replicatedimage is viewed, which is undesirable. Certain embodiments describedherein can be used to improve intensity distributions, and thereby, canbe used to improve the replicated image when viewed.

In the description that follows, like numerals or reference designatorswill be used to refer to like parts or elements throughout. In addition,the first digit of a three digit reference number, or the first twodigits of a four digit reference number, identifies the drawing in whichthe reference number first appears.

FIGS. 1A, 1B and 1C are front, top and side views, respectively, ofexemplary planar optical waveguide 100 that can be used to replicate animage associated with an input-pupil to an expanded output-pupil. Theterm “input pupil,” as used herein, refers to an aperture through whichlight corresponding to an image is overlaid on an input-coupler of awaveguide. The term “output pupil,” as used herein, refers to anaperture through which light corresponding to an image exits anoutput-coupler of a waveguide. The planar optical waveguide 100 willoften be referred to hereafter more succinctly simply as an opticalwaveguide 100, or even more succinctly as a waveguide 100. As will bediscussed in further detail below with reference to FIG. 2, the imagethat the waveguide 100 is being used to replicate, and likely alsoexpand, can be generated using a display engine.

Referring to FIGS. 1A, 1B and 1C, the planar optical waveguide 100includes a bulk-substrate 106 having an input-coupler 112 and anoutput-coupler 116. The input-coupler 112 is configured to couple lightcorresponding to an image associated with an input-pupil into thebulk-substrate 106 of the waveguide. The output-coupler 116 isconfigured to couple the light corresponding to the image associatedwith the input-pupil, which travels in the planar optical waveguide 100from the input-coupler 112 to the output-coupler 116, out of thewaveguide 100 so that the light is output and imaged from theoutput-pupil.

The bulk-substrate 106, which can be made of glass or optical plastic,but is not limited thereto, includes a first major planar surface 108and a second major planar surface 110 opposite and parallel to the firstmajor planar surface 108. The first major planar surface 108 canalternatively be referred to as the front-side major surface 108 (ormore simply the front-side surface 108), and the second major planarsurface 110 can alternatively be referred to as the back-side majorsurface 110 (or more simply the back-side surface 110). As the term“bulk” is used herein, a substrate is considered to be “bulk” substratewhere the thickness of the substrate (between its major surfaces) is atleast ten times (i.e., 10×) the wavelength of the light for which thesubstrate is being used as an optical transmission medium. For anexample, where the light (for which the substrate is being used as anoptical transmission medium) is red light having a wavelength of 620 nm,the substrate will be considered a bulk-substrate where the thickness ofthe substrate (between its major surfaces) is at least 6200 nm, i.e., atleast 6.2 μm. In accordance with certain embodiments, the bulk-substrate106 has a thickness of at least 25 μm between its major planar surfaces108 and 110. In specific embodiments, the bulk-substrate 106 has athickness (between its major surfaces) within a range of 25 μm to 1000μm. The bulk-substrate 106, and more generally the waveguide 100, istransparent, meaning that it allows light to pass through it so that auser can see through the waveguide 100 and observe objects on anopposite side of the waveguide 100 than the user's eye(s).

The planar optical waveguide 100 in FIGS. 1A, 1B and 1C is also shown asincluding an intermediate-component 114, which can alternatively bereferred to as an intermediate-zone 114. Where the waveguide 100includes the intermediate-component 114, the input-coupler 112 isconfigured to couple light into the waveguide 100 (and morespecifically, into the bulk-substrate 106 of the waveguide 100) and in adirection of the intermediate-component 114. The intermediate-component114 is configured to redirect such light in a direction of theoutput-coupler 116. Further, the intermediate-component 114 isconfigured to perform one of horizontal or vertical pupil expansion, andthe output-coupler 116 is configured to perform the other one ofhorizontal or vertical pupil expansion. For example, theintermediate-component 114 can be configured to perform horizontal pupilexpansion, and the output-coupler 116 can be configured to verticalpupil expansion. Alternatively, if the intermediate-component 114 wererepositioned, e.g., to be below the input-coupler 112 and to the left ofthe output-coupler 116 shown in FIG. 1A, then the intermediate-component114 can be configured to perform vertical pupil expansion, and theoutput-coupler 116 can be configured to perform horizontal pupilexpansion. In certain embodiments, the intermediate-component isconfigured as a fold-grating. In other embodiments, theintermediate-component is a mirror based component, rather than agrating based component.

The input-coupler 112, the intermediate-component 114 and theoutput-coupler 116 can be referred to collectively herein as opticalcomponents 112, 114 and 116 of the waveguide, or more succinctly ascomponents 112, 114 and 116.

It is possible that a waveguide includes an input-coupler and anoutput-coupler, without including an intermediate-components. In suchembodiments, the input-coupler would be configured to couple light intothe waveguide and in a direction toward the output-coupler. In suchembodiments, the output-coupler can provide one of horizontal orvertical pupil expansion, depending upon implementation.

In FIG. 1A, the input-coupler 112, the intermediate-component 114 andthe output-coupler 116 are shown as having rectangular outer peripheralshapes, but can have alternative outer peripheral shapes. For example,the input-coupler 112 can alternatively have a circular outer peripheralshape, but is not limited thereto. For another example, theintermediate-component can have a triangular or hexagonal outerperipheral shape, but is not limited thereto. Further, it is noted thatthe corners of each of the peripheral shapes, e.g., where generallyrectangular or triangular, can be chamfered or rounded, but are notlimited thereto. These are just a few exemplary outer peripheral shapesfor the input-coupler 112, the intermediate-component 114 and theoutput-coupler 116, which are not intended to be all encompassing.

As can best be appreciated from FIGS. 1B and 1C, the input-coupler 112,the intermediate-component 114 and the output-coupler 116 are all shownas being provided in or on a same surface (i.e., the back-side surface110) of the waveguide 100. In such a case, the input-coupler 112 can betransmissive (e.g., a transmission grating), the intermediate-component114 can be reflective (e.g., a reflective grating), and theoutput-coupler 116 can also be reflective (e.g., a further reflectivegrating). The input-coupler 112, the intermediate-component 114 and theoutput-coupler 116 can alternatively all be provided in the front-sidesurface 110 of the waveguide 100. In such a case, the input-coupler 112can be reflective (e.g., a reflective grating), theintermediate-component 114 can be reflective (e.g., a further reflectivegrating), and the output-coupler 116 can also be transmissive (e.g., atransmission grating).

Alternatively, the input-coupler 112, the intermediate-component 114 andthe output-coupler 116 can all be embedded (also referred to asimmersed) in the bulk-substrate 106. For example, the bulk-substrate 106can be separated into two halves (that are parallel to the majorsurfaces 108 and 110), and the input-coupler 112, theintermediate-component 114 and the output-coupler 116 can be provided in(e.g., etched into) one of the inner surfaces of the two halves, and theinner surfaces of the two halves can be adhered to one another.Alternatively, the bulk-substrate 106 can be separated into two halves(that are parallel to the major surfaces 108 and 110), and theinput-coupler 112, the intermediate-component 114 and the output-coupler116 can be provided between the inner surfaces of the two halves. Otherimplementations for embedding the input-coupler 112, theintermediate-component 114 and the output-coupler 116 in thebulk-substrate 106 are also possible, and within the scope of theembodiments described herein. It is also possible that one of theinput-coupler 112, the intermediate-component 114 and the output-coupler116 is provided in or on the front-side surface 108 of the waveguide108, another one of the components 112, 114 and 116 is provided in or onthe back-side surface 110, and the last one of the components 112, 114and 116 is embedded or immersed in the bulk-substrate 106. Moregenerally, unless stated otherwise, any individual one of theinput-coupler 112, the intermediate-component 114 and the output-coupler116 can be provided in or on either one of the major planar surfaces 108or 110 of the bulk-substrate 106, or embedded therebetween.

The input-coupler 112, the intermediate-component 114 and theoutput-coupler 116 can each be implemented as a diffraction grating, ormore generally, as a diffractive optical element (DOE). Such DOEs can beproduced using holographic processes, in which case, the DOEs can bemore specifically referred to a holographic optical elements (HOEs). Theinput-coupler 112 can alternatively be implemented as a prism, areflective polarizer or can be mirror based. Similarly, theoutput-coupler 116 can alternatively be implemented as a prism, areflective polarizer or can be mirror based. Depending upon the specificconfiguration and implementation, any one of the input-coupler 112, theintermediate-component 114 and the output-coupler 116 can be reflective,diffractive or refractive, or a combination thereof, and can beimplemented, e.g., as a linear grating type of coupler, a holographicgrating type of coupler, a prism or another type of optical coupler. Theintermediate-component 114, as noted above, can be implemented using afold-grating, or can alternatively be implemented as a mirror basedpupil expander, but is not limited thereto.

Where the input-coupler 112, the intermediate-component 114 and theoutput-coupler 116 are implemented in or on one (or both) of thesurfaces 108 and/or 110 of the waveguide 100, one or more of them can beimplemented as a surface grating, or more specifically, as a surfacerelief grating (SRG). A surface grating is a periodic structure in or onthe surface of an optical component, such as a bulk-substrate 106. Whenthe periodic structure is due to modulation of the surface itself, or acoating on the surface, it is referred to as a surface relief grating(SRG). An exemplary SRG includes uniform straight grooves in or on asurface of an optical component that are separated by uniform straightgroove spacing regions. The nature of the diffraction by an SRG dependsboth on the wavelength of light incident on the grating and variousoptical characteristics of the SRG, such as line spacing, groove depthand groove slant angle. An SRG can be fabricated by way of a suitablemicrofabrication process, which may involve etching of and/or depositionon a substrate (e.g., the bulk-substrate 106) to fabricate a desiredperiodic microstructure in or on the substrate to form an opticalcomponent, which may then be used as a production master such as a moldor mask for manufacturing further optical components. An SRG is anexample of a Diffractive Optical Element (DOE).

Where the input-coupler 112, the intermediate-component 114 and/or theoutput-coupler 116 is an SRG, each such SRG can be etched into one ofthe major planar surfaces 108 or 110 of the bulk-substrate 106. In suchembodiments, the SRG can be said to be formed “in” the bulk-substrate106. Alternatively, each SRG can be physically formed in an isotropiccoating that covers one of the major planar surfaces 108 or 110 of thebulk-substrate 106, in which case each such SRG can be said to be formed“on” the bulk-substrate 106. Either way, the components 112, 114 and 116are considered parts of the waveguide 100. In certain embodiments wherethe SRG(s) are formed in an isotropic coating, which covers one of themajor planar surfaces 108 or 110 of the bulk-substrate 106, theisotropic coating in which the SRG(s) is/are formed has a same index ofrefraction as the bulk-substrate 106. As will be discussed in furtherdetails below, with reference to FIG. 7, in accordance with specificembodiments of the present technology, one or more SRG(s) can be formedin an anisotropic coating, or more specifically, in a liquid crystalpolymer (LCP) coating, in which case the SRG(s) can be considered LCPbased SRG(s).

Referring specifically to FIG. 1A, in an exemplary embodiment, theinput-coupler 112 can have surface gratings that extend in a vertical(y) direction, the output-coupler 116 can have surface gratings thatextend in a horizontal (x) direction, and the intermediate-component 114can have surface gratings that extend diagonal (e.g., ˜45 degrees)relative to the horizontal and vertical directions. This is just anexample. Other variations are also possible and within the scope ofembodiments of the present technology.

More generally, the input-coupler 112, the intermediate-component 114and the output-coupler 116 can have various different outer peripheralgeometries, can be provided in or on either of the major planar surfacesof the bulk-substrate, or can be embedded in the bulk-substrate 106, andcan be implemented using various different types of optical structures,as can be appreciated from the above discussion, and will further beappreciated from the discussion below.

In general, light corresponding to an image, which is coupled into thewaveguide via the input-coupler 112, can travel through the waveguidefrom the input-coupler 112 to the output-coupler 114, by way of totalinternal refection (TIR). TIR is a phenomenon which occurs when apropagating light wave strikes a medium boundary (e.g., of thebulk-substrate 106) at an angle larger than the critical angle withrespect to the normal to the surface. In other words, the critical angle(θ_(c)) is the angle of incidence above which TIR occurs, which is givenby Snell's Law, as is known in the art. More specifically, Snell's lawspecifies that the critical angle (θ_(c)) is specified using thefollowing equation:

θ_(c)=sin⁻¹(n2/n1)

where

θ_(c) the critical angle for two optical mediums (e.g., thebulk-substrate 106, and air or some other medium that is adjacent to thebulk-substrate 106) that meet at a medium boundary,

n1 is the index of refraction of the optical medium in which light istraveling towards the medium boundary (e.g., the bulk-substrate 106,once the light is couple therein), and

n2 is the index of refraction of the optical medium beyond the mediumboundary (e.g., air or some other medium adjacent to the bulk-substrate106).

The concept of light traveling through the waveguide 100, from theinput-coupler 112 to the output-coupler 114, by way of TIR, can bebetter appreciated from FIG. 2, which is discussed below. Referring nowto FIG. 2, as in FIG. 1C, FIG. 2 shows a side view of the waveguide 100,but also shows a display engine 204 that generates an image includingangular content that is coupled into the waveguide by the input-coupler112. Also shown in FIG. 2, is representation of a human eye 214 that isusing the waveguide 100 to observe an image, produced using the displayengine 204, as a virtual image.

The display engine 204 can include, e.g., an image former 206, acollimating lens 208 and an illuminator 210, but is not limited thereto.The image former 206 can be implemented using a transmissive projectiontechnology where a light source is modulated by an optically activematerial, and backlit with white light. These technologies are usuallyimplemented using liquid crystal display (LCD) type displays withpowerful backlights and high optical energy densities. The illuminator210 can provide the aforementioned backlighting. The image former 206can also be implemented using a reflective technology for which externallight is reflected and modulated by an optically active material.Digital light processing (DLP), liquid crystal on silicon (LCOS) andMirasol® display technology from Qualcomm, Inc. are all examples ofreflective technologies. Alternatively, the image former 206 can beimplemented using an emissive technology where light is generated by adisplay, see for example, a PicoP™ display engine from Microvision, Inc.Another example of emissive display technology is a micro organic lightemitting diode (OLED) display. Companies such as eMagin and Microoledprovide examples of micro OLED displays. The image former 206, alone orin combination with the illuminator 210, can also be referred to as amicro display. The collimating lens 208 is arranged to receive adiverging display image from the image former 206, to collimate thedisplay image, and to direct the collimated image toward theinput-coupler 112 of the waveguide 100. In accordance with anembodiment, an entry pupil associated with the waveguide may beapproximately the same size as an exit pupil associated with the imageformer 206, e.g., 5 mm or less in some embodiments, but is not limitedthereto.

In FIG. 2, the display engine 204 is shown as facing the back-sidesurface 110 of the waveguide 100, and the eye 214 is shown as facing thefront-side surface 108 opposite and parallel to the back-side surface110. This provides for a periscope type of configuration in which lightenters the waveguide on one side of the waveguide 100, and exits thewaveguide at an opposite side of the waveguide 100. Alternatively, theinput-coupler 112 and the output-coupler 116 can be implemented in amanner such that the display engine 204 and the eye 214 are proximate toand face a same major planar surface (108 or 110).

The waveguide 100 can be incorporated into a see-through mixed realitydisplay device system, but is not limited to use therewith. A separateinstance of the waveguide 100 and the display engine 204 can be providedfor each of the left and right eyes of a user. In certain embodiments,such waveguide(s) 100 may be positioned next to or between see-throughlenses, which may be standard lenses used in eye glasses and can be madeto any prescription (including no prescription). Where a see-throughmixed reality display device system is implemented as head-mounteddisplay (HMD) glasses including a frame, the display engine 204 can belocated to the side of the frame so that it sits near to a user'stemple. Alternatively, the display engine 204 can be located in acentral portion of the HMD glasses that rests above a nose bridge of auser. Other locations for the display engine 204 are also possible. Inthese instances, the user can also be referred to as a wearer. Wherethere is a separate waveguide for each of the left and right eyes of auser, there can be a separate display engine for each of the waveguides,and thus, for each of the left and right eyes of the user. One or morefurther adjacent waveguides can be used to perform eye tracking based oninfrared light that is incident on and reflected from the user's eye(s)214, as is known in the art.

FIG. 3, which is similar to FIG. 1A in that it provides a front view ofthe waveguide 100, will now be used to explain how light that is coupledinto the waveguide 100 by the input-coupler 112, can travel by way ofTIR from the input-coupler 112 to the intermediate-component 114, and byway of TIR from the intermediate-component 114 to the output-coupler116, where it exits the waveguide 100. More specifically, as explainedin more detail below, a combination of diffractive beam splitting andTIR within the waveguide 100 results in multiple versions of an inputbeam of light 302(X) being outwardly diffracted from the output-coupler116 in both the length and the width of the output-coupler 116 as outputbeams 306(X) in respective outward directions (that is, away from thewaveguide 100) that substantially match the respective inward direction{circumflex over (k)}_(in)(X) of the corresponding input beam 302(X).

In FIG. 3, beams external to (e.g., entering or exiting) the waveguide100 are represented using shading and dotted lines are used to representbeams within (i.e., internal to) the waveguide 100. Perspective is usedto indicate propagation in the z-direction (i.e., towards or way from auser), with widening of the beams in FIG. 3 representing propagation inthe positive z (i.e., +z) direction (that is towards the user). Thus,diverging dotted lines represent beams within the waveguide propagatingtowards the front-side major surface 108 of the waveguide 100, with thewidest parts (shown as large dotted circles) represent those beamsstriking the front-side major surface 108 of the waveguide 100, fromwhich they are totally internally reflected back towards the back-sidemajor surface 110 of the waveguide 100, which is represented by thedotted lines converging from the widest points to the narrowest points(shown as the small dotted circles) at which they are incident on theback-side major surface 110 of the waveguide 100.

Exemplary regions where a beam is incident on the intermediate-component114 and splits into two beams, one of which travels in the horizontaldirection and the other one of which travels in the vertical direction,are labeled S (for split or splitting). Exemplary regions where a beamis incident on the output-coupler 116 and exits the waveguide 100 arelabeled E (for exit or exiting).

As illustrated, the input beam 302(X) is coupled into the waveguide 100,e.g., by way of diffraction, by the input-coupler 112, and propagatesalong a width of the input-coupler by way of TIR in the horizontaldirection. This results in the beam 302(X) eventually striking theintermediate-component 114 at a left-most splitting region (S). When thebeam 302(X) is incident at the left-most splitting region (S), thatincident beam 302(X) is effectively split in two, e.g., by way ofdiffraction. This splitting creates a new version of that beam 304(X)(specifically a first-order diffraction mode beam) which is directed ina generally downwards vertical (−y) direction towards the output-coupler116, in addition to a zero-order diffraction mode beam (i.e. unaffectedby the diffractive component) that continues to propagate along thewidth of the intermediate-component 114 in the horizontal (+x)direction, just as the beam would in the absence of theintermediate-component 114 (albeit at a reduced intensity). Thus, aportion of the beam effectively continues to propagate alongsubstantially the whole width of the intermediate-component 114,striking the intermediate-component 114 at various splitting regions(S), with another new version of the beam (in the same downwarddirection) created at each splitting region (S). As shown in FIG. 3,this results in multiple versions of the beam being directed toward, andincident on, the output-coupler 116, with the multiple versions of thebeam being horizontally separated so as to collectively spansubstantially the width of the output-coupler 116.

As also shown in FIG. 3, each new version of the beam as created at asplitting region (S) may itself strike the intermediate-component 114(e.g., a fold grating) during its downward propagation. This can resultin a splitting of the new version of the beam, e.g., by way ofdiffraction, to create a further new version of that beam that isdirected in a horizontal (+x) direction (which is a first-orderreflection mode beam), in addition to a zero-order diffraction mode beamthat continues to propagate in the downward vertical (−y) direction.This phenomenon may repeat numerous times within the waveguide, as canbe appreciated from FIG. 3. FIG. 3 is not drawn to scale, as many morereflections and splitting of beams are likely to occur than illustratedin FIG. 3, e.g., as can be better appreciated from FIG. 4.

In FIG. 3, the output-coupler 116 is shown as being located below theintermediate-component 114, and thus, the downward-propagating versionsof the beams will eventually be incident on the output-coupler 116, atwhich they are guided onto the various exit regions (E) associated withthe output-coupler 116. The output-coupler 116 is configured so thatwhen a version of the beam strikes the output-coupler, that beam isdiffracted to create a first-order diffraction mode beam directedoutwardly from the output-coupler 116, in an outward direction thatsubstantially matches the unique inward direction in which the originalbeam 302(X) corresponding to an image point X was input. Because thereare multiple versions of the beam propagating downwards thatsubstantially span the width of the output-coupler 116, multiple outputbeams 306(X) are generated across the width of the output-coupler 116(as shown in FIG. 3) to provide effective horizontal beam expansion,which can also be referred to as horizontal pupil expansion.

Moreover, the output-coupler 116 is configured so that, in addition tothe outwardly diffracted beams 306(X) being created at the various exitregions (E) from an incident beam, a zero-order diffraction mode beamcontinues to propagate downwards in the same specific direction as thatincident beam. This, in turn, strikes the output-coupler 116 at lowerportions thereof in the manner illustrated in FIG. 3, resulting in bothcontinuing zero-order and outward first-order beams. Thus, multipleoutput beams 306(X) are also generated across substantially the entireheight of the output-coupler 116 to provide effective vertical beamexpansion, which can also be referred to as vertical pupil expansion.

The output beams 306(X) are directed outwardly in outward directionsthat substantially match the unique input direction in which theoriginal beam 302(X) is inputted. In this context, substantiallymatching means that the outward direction is related to the inputdirection in a manner that enables a user's eye to focus any combinationof the output beams 306(X) to a single point on the retina, thusreconstructing the image point X from which the original beam 302(x)propagated or was otherwise emitted.

For a planar waveguide (i.e., a waveguide whose front-side and back-sidemajor surfaces lie substantially parallel to the xy-plane in theirentirety), the output beams 306(S) are substantially parallel to oneanother and propagate outwardly in an output propagation direction{circumflex over (k)}_(out) that is parallel to the unique inwarddirection {circumflex over (k)}_(in)(X) in which the corresponding inputbeam 302(X) was directed to the input-coupler 112. That is, directingthe beam 302(X) corresponding to the image point X to the input-coupler112 in the inward direction {circumflex over (k)}_(in)(X) causescorresponding output beams 306(X) to be directed (e.g., diffracted)outwardly and in parallel from the output-coupler 116, each in anoutward propagation direction {circumflex over (k)}_(out)(X)={circumflexover (k)}_(in)(X) due to the configuration of the waveguide 100.

In the exemplary implementation described above, theintermediate-component 114 (e.g., a fold grating) is configured toprovide horizontal pupil expansion, also referred to as effectivehorizontal beam expansion; and the output-coupler 116 is configured toprovide vertical pupil expansion, also referred to as effective verticalbeam expansion. Alternatively, the intermediate-component 114 can berepositioned, e.g., below the input-coupler 112 and to the side of theoutput-coupler 116, and the components 112, 114 and 116 can bereconfigured such that the intermediate-component 114 is configured toprovide vertical pupil expansion, and the output-coupler 116 isconfigured to provide horizontal pupil expansion, as was noted above.While there are significant benefits to performing horizontal (orvertical) pupil expansion using the intermediate-component 114, thevarious zero-order and first-order diffraction modes caused by theintermediate-component 114 result in multiple-loop interference, whichis explained below with reference to FIG. 4.

FIG. 4 is illustrative of the intermediate-component 114 of thewaveguide 100, but does not show other components of the waveguide, suchas the input-coupler 112 and the output-coupler 116. Referring to FIG.4, the dark lined loops shown therein, which are labeled IL, areillustrative of multiple interference loops that occur within theintermediate-component 114, which can collectively be referred to asmultiple-loop interference. Each of the multiple interference loops isanalogous to the type of interference that occurs using a Mach-Zehnderinterferometer. In each interference loop IL, the positions where twoarrow heads meet are illustrative of positions where zero-order andfirst-order reflections of an input beam (e.g., the input beam 302(X))are incident on same locations of the intermediate-component 114 at asame time. Such dark lines with arrows are representative of pathways oflight traveling within intermediate-component 114 of the waveguide 100.If the optical-length of each pathway (also known as an optical pathlength) were the same, then when the light beams traveling to the samepoint via different pathways are recombined they would add in a mannerthat results in constructive interference. More specifically, when beamsof light from different paths have the same optical path lengths and thesame polarization orientation and are imaged onto the same part of aretina of a human eye, the light constructively interferes and intensityis equal to the scalar sum of the beams. However, due to mechanicaltolerances between the different pathways, the path length of the lightfollowing different pathways to a same location (on theintermediate-component 114) will actually be different, which can resultin (total or partial) destructive interference, which causes theintensity of the light to diminish when imaged by a user's eye. Morespecifically, when beams of light from different paths have differentoptical path lengths and are imaged onto the same part of a retina of ahuman eye, the light destructively interferes and intensity is less thanthe scalar sum of the beams. Such destructive interference can causedark fringes, and more generally, can cause a non-uniform intensitydistribution in the light that eventually reaches the output-coupler 116and exits the waveguide 100. More generally, the multiple-loopinterference, if not compensated for, can cause variations in intensitythat would be perceptible to a human eye viewing an image that isreplicated using the waveguide, which is undesirable.

Depending on the orientation of the various components 112, 114 and 116of the waveguide, these components may diffract light of incidentpolarization at different intensities. For example, there can be anapproximately five-to-one (i.e., ˜5:1) difference between orthogonalhorizontal and vertical diffraction efficiency. If the incidentpolarization is not optimized for specific grating line orientations ofthe various components 112, 114 and 116 at certain angles, diffractionefficiency can suffer, which can cause dark areas to occur in an imagethat is replicated using the waveguide and being viewed by a human eye,which is undesirable.

The polarization of light specifies the orientation of the plane thatthe light wave's electric field oscillates in. Explained another way,the polarization of light is the state of its electric field vector(e-vector) orientation. Light can, for example, be non-polarized (acompletely disordered, chaotic orientation of the e-vector), linearlypolarized (e-vector oscillates in a plane that is constant), circularlypolarized, or elliptical polarized. Linearly polarized light can be,e.g., horizontally polarized light or vertically polarized light, but isnot limited thereto. The type of polarization that is ideal in animaging system depends on many factors, including, e.g., the types andorientations of the components 112, 114 and 116. For a specific example,referring briefly back to FIG. 1A, assume that each of the components112, 114 and 116 is an SRG type DOE that including grating lines.Further, assume that the input-coupler 112 includes vertical gratinglines, and intermediate-component 114 includes 45 degree (diagonal)grating lines, and the output-coupler includes horizontal grating lines.In such an imaging system, the light that is incident on theinput-coupler 112 would ideally be vertically polarized; theintermediate-component 114 would ideally rotate the polarization of thelight by precisely 90 degrees (so that it becomes horizontallypolarized); and that light when incident on the output-coupler 116(where it is out coupled from the waveguide 100) would ideally behorizontally polarized. However, this is not what would typically occur.The intermediate-component 114 (e.g., gratings thereof) will cause amajority of the polarization rotation, but TIR also causes anangularly-dependent polarization rotations. Further, the input-coupler112 and output-coupler 116 can also cause some undesired polarizationrotation. In other words, in such an implementation theintermediate-component 114 does not simply rotate the polarization ofall the light that it diffracts by precisely 90 degrees, and thus, thisresults in a polarization non-uniformity across the output-coupler 116.

The exemplary waveguide 100 shown in and described with reference toFIGS. 1-4 is for use in an imaging system that relies on pupilreplication. In such systems, i.e., systems that rely on pupilreplication, the output pupils are preferably uniformly overlapping forall angles. When this is not the case, e.g., because pupils are spacedtoo far apart from one another, angular-dependentspatial-non-uniformities in intensity arise, which manifest themselvesas bright and dark image artifacts, which are undesirable.

FIG. 5A is used to conceptually illustrate how a pupil, represented bythe solid-lined circle 502, is replicated, as light travels by way ofTIR from the input-coupler 112 to the intermediate-component 114, and byway of TIR from the intermediate-component 114 to the output-coupler116, where it exits the waveguide 100. In FIG. 5A, each of thedotted-lined circles represents a replication of the pupil 502, whichmay also be referred to simply as a pupil. While represented as circlesin FIG. 5A, each pupil is actually a collection of angles. When lightexits the waveguide 100, proximate the output-coupler 116, a human eye,which has a lens in it, receives the collection of angles associatedwith a pupil and coverts it back to an image, e.g., the image producedby the display engine 204 in FIG. 2. Where the waveguide 100, and morespecifically the components 114 and/or 116 thereof is/are configured toperform pupil expansion, when an expanded pupil and is converted to animage (by the lens of a human eye), the resulting image is expandedrelative to the original image (e.g., produced by the display engine 204in FIG. 2).

FIG. 5B conceptually illustrates an exemplary pupil distribution alongthe dashed line B-B shown in FIG. 5A, which pupil distribution is shownas having a generally sinusoidal function, due to each pupil have aGaussian intensity distribution and adjacent pupils only slightlyoverlapping one another. If the pupils were so spread apart that theydid not overlap at all, and each of the pupils had a top-hat intensitydistribution, then the pupil distribution can potentially have a squarewave function, e.g., as shown in FIG. 5C, although a sinusoidal function(an example of which is shown in FIG. 5B) is more likely. Pupildistributions having a sinusoidal or square wave function will manifestthemselves as bright and dark image artifacts, which are undesirable.Optimally, the pupils will overlap one another to achieve a uniformpupil distribution, which provides for a uniform intensity distributionfunction, as shown in FIG. 5D, which can be achieved, e.g., if there wasa 50% overlap between pupils. More generally, there is a desire tohomogenize pupil overlap to provide a substantially uniform pupildistribution in the light traveling within the waveguide that isincident on the output-coupler 116.

FIG. 6 is used to illustrate that non-uniformities in local and globalintensity which may occur when performing imaging using an opticalwaveguide, wherein the non-uniformities can occur due to multiple-loopinterference, non-optimal polarization and/or non-uniform pupildistribution. More specifically, the dark and light generally diagonalfringes are illustrative of non-uniformities in local intensity thatoccur do to the pupil distribution being non-uniform, and the darkblotches (shown primarily on the right side) are illustrative ofnon-uniformities in local intensity that occur due to multiple-loopinterference.

Embodiments of the present technology, which are described below, can beused to compensate for multiple-loop interference, provide for moreoptimized polarization and/or provide for a more uniform pupildistribution. More generally, embodiments of the present technology,which are described below, are utilized to cause the light that isoutput from a waveguide (e.g., 100) by an output-coupler (e.g., 116) tohave a more uniform intensity distribution, so that any non-uniformityin intensity is imperceptible to a human eye viewing an image using thewaveguide.

Certain embodiments described herein compensate for multiple-loopinterference, and more specifically mitigate the adverse effects ofmultiple-loop interference, by utilizing polarization rotations and/orwave front phase diversity. If two beams of coherent polarized lightfollowing different paths are recombined, but the polarization of a beamfollowing one path is rotated by 90 degrees relative to a beam followingthe other path, then the two beams will not interfere with one anotherwhen they are recombined. Accordingly, orthogonal polarization of lightin one path versus another path causes that the light to interact lesswhen imaged onto the same point on a retina of a human eye, which isadvantageous. Certain embodiments of the present technology, describedbelow, rely on this phenomenon to mitigate the adverse effects they mayotherwise be caused by multiple-loop interference. Certain embodimentsadditionally, or alternatively, provide enough wave front phasediversity such that effects of destructive interference (e.g., due todifferent light beams imaged on the same portion of a retina beingcompletely out of phase) become averaged out.

Without utilizing one or more of the embodiments of the presenttechnology described herein, the light traveling within the waveguideand incident on the output-coupler, would likely have a generallyhomogeneous polarization, and more specifically, would have onepolarization that is quite dominant compared to the other. Embodimentsof the present technology can be used to provide, for light travelingwithin the waveguide and incident on the output-coupler, a ratio ofhorizontally polarized light to vertically polarized light, or viceversa, of no more than 2 to 1, and preferably about 1 to 1. For lightincident on the output-coupler (after having traveled through thewaveguide), where the ratio of horizontally polarized light tovertically polarized light, or vice versa, is not more than 2 to 1, suchlight is considered to have a substantially heterogeneous polarizationdistribution.

In accordance with certain embodiments, the phases of wave fronts oflight traveling through a waveguide are offset relative to one anotherto achieve an averaging between constructive and destructiveinterference. More specifically, in accordance with certain embodiments,sufficient wave front phase diversity is achieved such that lightexiting the waveguide, at its output-coupler, has a substantiallyheterogeneous phase in its wave fronts, so that there is a substantiallyuniform distribution, between 0 and 2π radians, of the phases of thewave fronts of light.

More generally, embodiments of the present technology described hereinare used to achieve a substantially uniform intensity distribution inthe light that exits a waveguide (e.g., 100) via an output-coupler(e.g., 116). A substantially uniform intensity distribution can be asubstantially uniform angular intensity distribution, or a substantiallyuniform spatial intensity distribution, depending upon implementation.It is also possible that substantially uniform intensity distributioncan be both a substantially uniform angular intensity distribution, anda substantially uniform spatial intensity distribution. A substantiallyuniform angular intensity distribution is especially beneficial inapplications where the location of a user's eye(s) is/are fixed relativeto the waveguide(s), e.g., in a head-mounted-display (HMD) or othernear-eye-display (NED) application. A substantially uniform spatialintensity distribution is especially beneficial in applications wherethe location of a user's eye(s) is/are not fixed relative to thewaveguide(s), e.g., in a heads-up-display (HUD) application. The overallgoal of having the light, output by the waveguide, having asubstantially uniform intensity distribution is so that anynon-uniformity in intensity is imperceptible to a human eye viewing animage using the waveguide.

An intensity distribution can have both a local intensity distributionand a global intensity distribution. The local intensity distributionrefers to a distribution of intensities associated with portions of animage that are relatively close to one another, e.g., associated withadjacent pixels and/or adjacent angular content of an image. The globalintensity distribution refers to a distribution of intensitiesassociated with an entire image, which includes pixels and/or angularcontent of an image that are relative far apart.

Without using embodiments of the present technology, or alternativetechniques for compensating for non-uniform intensity distributions (ifsuch alternative techniques exist), the light that is output from awaveguide by an output-coupler will have a non-uniform intensitydistribution that would be very noticeable to a human eye viewing animage that is reproduced using the waveguide. More specifically, certainportions of an image would appear significantly brighter than otherportions, and certain portions of the image would appear significantlydarker than other portions. An example of this can be appreciated fromFIG. 6, discussed above.

More specifically, without using embodiments of the present technology,or alternative techniques for compensating for non-uniform intensitydistributions (if such alternative techniques exist), there would likelybe at least a ten-percent change in intensity per degree in the angularcontent of an image, e.g., such as in adjacent pixels of an image. Inother words, the local intensity distribution would likely becharacterized by at least a ten-percent change in intensity per degreein the angular content of the image. Further, without using embodimentsof the present technology, or alternative techniques for compensatingfor non-uniform intensity distributions (if such alternative techniquesexist), there would likely be at least a sixty-percent change inintensity over the entire angular content of an image. In other words,the global intensity distribution would likely be characterized by atleast a sixty-percent change in intensity over the entire angularcontent of the image.

Embodiments of the present technology, which are described herein, areintended to be used to provide for a substantially uniform intensitydistribution, wherein variations in intensity would be imperceptible toa human eye viewing an image that is replicated using a waveguide. Morespecifically, embodiments of the present technology can be used toprovide a substantially uniform intensity distribution in light that isoutput from a waveguide by an output-coupler (e.g., 116), which meansthat there is no more than a two-percent change in intensity per degreein the angular content of an image (e.g., such as in adjacent pixels ofan image) and there is no more than a thirty-percent change in intensityover the entire angular content of the image. In other words,embodiments of the present technology can be used to achieve a localintensity distribution characterized by no more than a two-percentchange in intensity per degree in the angular content of the image, aswell as to achieve a global intensity distribution characterized by nomore than a thirty-percent change in intensity over the entire angularcontent of an image. Accordingly, embodiments of the present technologycan be used to improve local uniformity by at least a factor of five,and to improve the global uniformity by at least a factor of two,compared to if such embodiments were not used.

Liquid Crystal Polymer (LCP) Coating

Referring now to FIG. 7, in accordance with certain embodiments of thepresent technology, a waveguide 700 includes a liquid crystal polymer(LCP) coating 702 is provided on at least one of the major planarsurfaces (e.g., 108) of the bulk-substrate 106. In such embodiments, theLCP coating 702 will induce spatially-dependent polarization changes inbeams of light that are incident on the LCP coating 702 while travelingthrough the bulk-substrate 106 of the waveguide 100 by means of TIR. TheLCP coating 702 can be added to the waveguide 100 to provide moreheterogeneous polarization and compensate multiple-loop interferencecaused by the intermediate-component 114. Additionally, if the LCPcoating 702 is thick enough to increase wave front phase diversity, thenthe LCP coating 702 can also provide for a more uniform pupildistribution.

The LCP coating 702 is an optically anisotropic and birefringentmaterial that has an index of refraction (also known as a refractiveindex) that depends on the polarization and propagation direction oflight. Accordingly, when light travelling within the bulk-substrate 106is incident on the LCP coating 702, the birefringence of the coatingcauses the light to be split by polarization into two rays takingslightly different paths. Considering the combined transverse electric(TE) and transverse magnetic (TM) modes of the light propagating throughthe waveguide 100, the LCP coating 702 acts as retarder (i.e.,polarization rotator) to the polarization state of light propagatingthrough it. The degree of retardation (i.e., polarization rotation) is afunction of the alignment of the liquid crystal molecules and thethickness of the LCP coating 702, which can also be referred to as anLCP film. When light propagates through the LCP coating the polarizationstate is changed and two beams of light that would otherwisedestructively interfere (without the LCP coating) will no longerdestructively interfere, which helps improve the uniformity of theoutput.

In certain embodiments, the LCP coating 702 has a uniaxialbirefringence, which means that there is a single direction governingthe optical anisotropy whereas all directions perpendicular to thesingle direction (or at a given angle relative to the single direction)are optically equivalent. Where the LCP coating has a uniaxialbirefringence, the LCP coating has a different index of refraction alongone of three axis (e.g., the index of refraction in an x-directiondiffers from the index of refraction in the y- and z-directions). Inother embodiments, the LCP coating has a biaxial birefringence, in whichcase the LCP coating can have a different index of refraction along allthree axis.

Where the components 112, 114 and 116 are all provided in or on a samemajor planar surface (e.g., 110) of the bulk-substrate 106, the LCPcoating can be applied on the opposite major planar surface (e.g., 108),as shown in FIG. 7. Where the components 112, 114 and 116 are embeddedin the bulk-substrate 106, the LCP coating can be applied on one or bothof the major planar surfaces (e.g., 108 and/or 110). Where at least oneof the components 112, 114 or 116 is provided in or on one of the majorplanar surfaces (e.g., 110), and at least another one of the components112, 114 or 116 is provided in or on the other one of the major planarsurfaces (e.g., 108), then an LCP coating can be provide on oppositesides of any one of (or all of) the components 112, 114 and 116, e.g.,such that an LCP coating overlaps (partially or completely) one of (orall of) the components 112, 114 and 116. In other words, a first LCPcoating can cover one or more portions of one of the major planarsurfaces (e.g., 110), and a second LCP coating can cover one or moreportions of the other one of the major planar surfaces (e.g., 108). Thetwo LCP coatings can both be made of the same LCP coating material, orof different LCP coating materials, and the thicknesses of the two LCPcoatings may be the same, or different than one another.

The LCP coating 702 can cover an entire major planar surface(s) (e.g.,108 and/or 110), as shown in FIG. 7, or just portions thereof. Forexample, the LCP coating 702 can cover a portion of a major planarsurface that spatially overlaps (in the x and y directions) the entireinput-coupler 112 (or overlaps just a portion of the input-coupler 112),a portion of a major planar surface that spatially overlaps the entireintermediate-component 114 (or overlaps just a portion of theintermediate-component 114), and/or a portion of a major planar surfacethat spatially overlaps the entire output-coupler 116 (or overlaps justa portion of the output-coupler 116).

In accordance with specific embodiments, a thickness of the LCP coating702 is within a range of about 100 nm to 1500 nm. Accordingly, in suchembodiments the LCP coating 702 is significantly thinner than thebulk-substrate 106. Where an LCP coating is provided on both majorplanar surfaces of a waveguide, the thickness of the LCP coatings can bethe same, or different from, one another, as noted above. Further, asnoted above, the types of LCP coatings can be the same as, or differentthan, one another.

If an LCP coating only coincides with the input-coupler 112, or portionsthereof, then the LCP coating would help randomize the polarization oflight beams that enter the waveguide 100 through the input-coupler 112,as portions of such light reflect off a boundary 704 between thebulk-substrate 106 and the LCP coating 702, and other portions of suchlight diffract into the LCP coating 702. In other words, in such anembodiment, the LCP coating 702 would help provide a heterogeneouspolarity distribution of light traveling within and eventually exitingthe waveguide. However, if the LCP coating does not coincide with theintermediate-component 114, then the LCP coating would not mitigate theadverse effects of multiple-loop interference described above, e.g.,with reference to FIG. 4.

The LCP coating 702 can be patterned with a defined orientationthroughout the coating. Patterning of the molecules can occur in anydimension of the LCP coating, and could also be uniform or completelyrandom. The thickness of the LCP coating could vary from very thin (˜100nm) to very thick (>1 μm), as mentioned above. The LCP coating can bepatterned using photoalignment layers or other liquid crystal alignmenttechniques, such as, but is not limited to, rubbed polyimides, physicalrelief structures on a glass surface, monolayer coatings, etc. Theproperties of the LCP coating that can be tuned include, but are notlimited, the coating thickness, extraordinary and ordinary indices ofrefraction, liquid crystal angles, periodicity in any dimension ofpatterning, directionality of patterning relative to surface reliefgratings, sharpness of features between patterned and non-patterned areaof liquid crystal, etc.

Mismatched Index of Refraction Coating or Substrate

Referring now to FIG. 8, in accordance with certain embodiments of thepresent technology, a waveguide 800 includes a transparent planaroptical-component 802 that has a different index of refraction than thebulk-substrate 106 (in or on which the components 112, 114 and 116 areformed) and is located adjacent to and adhered to one of the majorplanar surfaces 108 or 110 of the bulk-substrate 106. More specifically,the bulk-substrate 106 has an index of refraction n1, and theoptical-component has an index of refraction n2, where n2≠n1. Thethickness of the planar optical-component 802, which can also bereferred to as the adjacent optical-component 802, is at least ten times(i.e., 10×) the wavelength of the light for which the substrate is beingused as an optical transmission medium, and thus, the planar-opticalcomponent 802 is also a bulk-substrate, albeit a differentbulk-substrate than the bulk-substrate 106 (in or on which thecomponents 112, 114 and 116 are formed). Stated another way, theadjacent planar optical-component 802 is a coating or substrate (e.g., aplate) that has a mismatched index of refraction relative to thebulk-substrate 106 (in or on which the components 112, 114 and 116 areformed).

Optical components are considered to have different indexes ofrefraction from one another so long as their respective indexes ofrefraction differ from one another by at least 0.05. Conversely, opticalcomponents are considered to have substantially the same indexes ofrefraction if their respective indices of refraction differ from oneanother by less than 0.05. Optical components are considered to havesignificantly different indexes of refraction, as the term is usedherein, if their respective indexes of refraction differ from oneanother by at least 0.20.

In FIG. 8, reference 804 represents the physical boundary between thebulk-substrate 106 and the adjacent planar optical-component 802. Theadjacent planar optical-component 802 can be made of glass or opticalplastic. Alternatively, adjacent planar optical-component 802 can be acoating that is deposited on one of the major planar surfaces 108 or 110of the bulk-substrate 106. In certain embodiments, the adjacent planaroptical-component 802 is made of an isotropic material, in which casethe planar optical-component 802 has the same optical properties in alldirections (e.g., the x, y and z directions). In other embodiments, theadjacent planar optical-component 802 is made of an anisotropicmaterial, in which case the planar optical-component 802 has thedifferent optical properties in different directions (e.g., the opticalproperties in the x direction differ from the optical properties in atleast one of the y and z directions). In a specific example, the planaroptical-component 802 that has a mismatched index of refraction relativeto the bulk-substrate 106 (in or on which the components 112, 114 and116 are formed) can be an LCP coating. In other words, the LCP coating702 (described above with reference to FIG. 7) can be the planaroptical-component 802 having a mismatched index of refraction relativeto the bulk-substrate 106 (which is described with reference to FIG. 8).

In certain embodiments, the adjacent planar optical-component 802,whether made of an isotropic material or an anisotropic material, can beconfigured to act as a selective reflector for certain polarizationsand/or angles of light. Where the adjacent planar optical-component 802is anisotropic, the axial component of the coating can be applied indifferent geometries relative to the waveguide geometry (in dependenceon the direction of different DOEs) to optimize performance.

Referring specifically to FIG. 8, the arrowed solid lines 806 arerepresentative of light that is coupled into the bulk-substrate 106 (bythe input-coupler 112) and propagates through the bulk-substrate 106having the index of refraction n1, towards the boundary 804 (between thebulk-substrate 106 and the adjacent planar optical-component 802 havingthe index of refraction n2). As specified by the Fresnel equations andSnell's law, where light traveling within the bulk-substrate 106 isincident on the boundary 804 at an angle of incidence that is below thecritical angle (as specified by Snell's law), a first portion of thelight that is incident on the boundary 804 (between the bulk-substrate106 and the adjacent planar optical-component 802) reflects off theboundary 804 and remains in the bulk-substrate 106, and a furtherportion of the light that travels within the bulk-substrate 106 and isincident on the boundary 804 is refracted into the adjacent planaroptical-component 802. In FIG. 8, the arrowed dashed lines 808correspond to light that is reflected at the boundary 804, and thearrowed dotted lines 810 correspond to light that is refracted at theboundary 804. After further reflections (by the major planar surface ofthe planar optical-component 802 opposite the boundary 804), some ofthat light will be reflected off the boundary 804 (between thebulk-substrate 106 and the adjacent planar optical-component 802) andremain within the adjacent planar optical-component 802, and some ofthat light will be refracted back into the bulk-substrate 106. Thisphenomena will continue along the length of the waveguide such that someportions of the light will travel different path lengths than otherportions of the light. This will have the effect of providing for wavefront phase diversity that can provide for a uniform wave front phasedistribution of the light by the time the light is incident on theoutput-coupler 116. It is noted that only a few of the reflections andrefractions of light are shown in FIG. 8, so as to not make the figuretoo cluttered. Where light traveling within the bulk-substrate andincident on the boundary 804 is above the critical angle (as specifiedby Snell's law), the light that is incident on the boundary 804 (betweenthe bulk-substrate 106 and the adjacent planar optical-component 802)with experience TIR, and none of that light will be refracted into theadjacent planar optical-component 802.

Where the waveguide includes an intermediate-component 114 that issusceptible to multiple-loop interference, which was described abovewith reference to FIG. 4, there are benefits to the light (that is to beimaged onto the same point on a retina of a human eye) travellingnumerous different path lengths before being recombined. As noted above,if the beams of light from different paths have the same optical pathlengths and the same polarization orientation and are imaged onto thesame part of a retina of a human eye, the light constructivelyinterferes and intensity is equal to the scalar sum of the beams, whichwould be advantageous, but would be very difficult to achieve inpractice for all possible optical paths. Conversely, if the beams oflight from different paths have the different optical path lengths, suchthat they are exactly 180 degrees out of phase, with the samepolarization orientation, total destructive interference would occur,essentially destroying the image or pupil intended by be replicatedusing the waveguide. More specifically, if two beams of coherent lightare completely (i.e., 180 degrees, or π radians) out of phase, thendestructive interference will occur if the beams of light are imagedonto the same point of a retina of a human eye, which would result indark image artifacts, which are undesirable. By causing light (that isto be imaged onto the same point on a retina of a human eye) to travelthrough multiple different path lengths, through use of the adjacentplanar optical-component 802 (which has a mismatched index of refractionrelative to the bulk-substrate 106 in or on which the components 114,116 and 118 are included), destructive interference will be averagedout, which has the beneficial effect of compensating for themultiple-loop interference. In other words, one of the purposes ofadding the adjacent planar optical-component 802, which has a mismatchedindex of refraction relative to the bulk-substrate 106 (in or on whichthe components 112, 114 and 116 are formed), is to compensate for themultiple-loop interference caused by the intermediate-component 114.

Another one of the purposes of adding the adjacent planaroptical-component 802, which has a mismatched index of refractionrelative to the bulk-substrate 106 (in or on which the components 112,114 and 116 are formed), is to improve and preferably achieve asubstantially uniform pupil distribution, or more generally, to decreasepupil replication artifacts. For example, referring back to FIGS. 5A-5D,adding the adjacent planar optical-component 802, which has a mismatchedindex of refraction relative to the bulk-substrate 106, can be used tochange a waveguide that would otherwise having a pupil distributioncorresponding to the functions shown in FIG. 5B or 5C into asubstantially uniform pupil distribution function, as shown in FIG. 5D.

In certain embodiments, the index of refraction n2 of the adjacentplanar optical-component 802 is greater than the index of refraction n1of the bulk-substrate (i.e., n2>n1). In other embodiments, the index ofrefraction n2 of the adjacent planar optical-component 802 is less thanthe index of refraction n1 of the bulk-substrate (i.e., n2<n1). Wherethe index of refraction n2 of the adjacent planar optical-component 802is less than the index of refraction n1 of the bulk-substrate 106, thereis a further advantage as there is a secondary TIR condition. Forexample, if n1=1.7 and n2=1.5, the critical angle where TIR occurs is62.9 degrees relative to a normal to the boundary 804. Accordingly,light traveling within the bulk-substrate 106 that is incident on theboundary 804 having an angle of incidence (relative to the normal to theboundary 804) that is above 62.9 degrees never refracts out of thebulk-substrate 106 into the adjacent planar optical-component 802. Thesehigh angles of incidence are most problematic for pupil replication. Inthese embodiments, the apparent thickness of the waveguide will be lessfor light having high angles of incidence compared to for light havinglower angles of incidence, where the light, or at least portionsthereof, will propagate through both the bulk-substrate 106 and theadjacent planar optical-component 802. Accordingly, the distance betweenthe reflection nodes will be shorter for light beams having high anglesof incidence (compared to light beams having lower angles of incidence)and the spatial profile of the output distribution will be morehomogeneous due to more closely overlapped pupils.

The adjacent planar optical-component 802 (that has a mismatched indexof refraction relative to the bulk-substrate 106) can be attached orotherwise applied to the bulk-substrate 106 in various differentmanners. For example, where implemented as a coating material, thecoating material can be applied through various manufacturing processesincluding, but is not limited to, lamination, wet coating (e.g., spincoating), deposition techniques, etc.

In FIG. 8, the adjacent planar optical-component 802 (that has amismatched index of refraction relative to the bulk-substrate 106) isshown as being added adjacent to only one of the major planar sides ofthe bulk-substrate 106. In other embodiments, two adjacent planaroptical-components (that have a mismatched index of refraction relativeto the bulk-substrate 106) can be added so that they are adjacent toboth major planar side of the bulk-substrate 106 (i.e., one adjacent toeach opposing side). In such embodiments, the two adjacent planaroptical-components, added adjacent to opposing both major planar sidesof the bulk-substrate 106, can have the same index of refraction as oneanother, or different indexes of refraction than one another. In stillother embodiments, the bulk-substrate 106 can be separated into twohalves (that are parallel to the major surfaces 108 and 110), and theplanar optical-component 802 (that has a mismatched index of refractionrelative to the bulk-substrate 106) can be embedded between the twohalves, where it can act as a volume layer.

Liquid Crystal Polymer (LCP) Based Surface Relief Grating (SRG)

A diffraction grating is an optical component with a periodic structure.When the periodic structure is on the surface of an optical component,it is referred to a surface grating. When the periodic structure is dueto varying of the surface itself, it is referred to as a surface reliefgrating (SRG). For example, an SRG can include uniform straight groovesin a surface of an optical component that are separated by uniformstraight groove spacing regions. Groove spacing regions can be referredto as “lines”, “grating lines” or “filling regions”. The nature of thediffraction by an SRG depends both on the wavelength of light incidenton the SRG and various optical characteristics of the SRG, such as linespacing, groove depth and groove slant angle. An SRG can be fabricatedby way of a suitable microfabrication process, which may involve etchingof and/or deposition on a substrate to fabricate a desired periodicmicrostructure on the substrate to form an optical component, which maythen be used as a production master such as a mold or mask formanufacturing further optical components. An SRG is an example of aDiffractive Optical Element (DOE). When a DOE is present on a surface(e.g. when the DOE is an SRG), the portion of that surface spanned bythat DOE can be referred to as a DOE area.

As noted above, in the discussion of FIGS. 1A-1C, the input-coupler 112,the intermediate-component 114 and/or the output-coupler 116 can be anSRG. Where this is the case, an SRG can be formed “in” thebulk-substrate 106 by etching the SRG into one of the major planarsurfaces 108 or 110 of the bulk-substrate 106, or an SRG can be formed“on” the bulk-substrate 108 by formed the SRG in an isotropic coatingthat covers one of the major planar surfaces 108 or 110 of thebulk-substrate 106.

In specific embodiments of the present technology, rather than formingSRG(s) in an isotropic coating that covers one of the major planarsurfaces 108 or 110 of the bulk-substrate 106, one or more of the SRG(s)are instead formed in a liquid crystal polymer (LCP) coating.Accordingly, where any of the components 112, 114 or 116 is an SRGformed in an LCP coating, the component can be referred to as an LCPbased SRG. In other words, referring back to FIGS. 1A, 1B and 1C, anyone, two, or all of the input-coupler 112, the intermediate-component114 and the output-coupler 116 can be implemented as an LCP based SRG.In such embodiments, effects of an SRG being made from an LCP wouldoccur at every interaction of light with the LCP based SRG.

An LCP coating, as noted above in the discussion of the embodimentsdiscussed with reference to FIG. 7, is an optically anisotropic andbirefringent material that has an index of refraction (also known as arefractive index) that depends on the polarization and propagationdirection of light. More specifically, whereas an isotropic polymercoating has a uniform index of refraction in all directions, ananisotropic birefringent LCP coating has different indices of refractionalong at least one axis of the material (one axis differs from the othertwo for uniaxial birefringent materials; and all three axis could bedifferent for bi-axial birefringent materials).

Forming one or more of the components 112, 114 and/or 116 as an LCPbased SRG enables more control of the refraction/diffraction of lightincident on the SRG. This is because different polarizations and anglesof propagation will experience different indices of refraction of theLCP based SRG and could result in differences in diffraction efficiencyand uniformity.

The LCP in which SRG(s) is/are formed could be aligned through alignmentlayers or holographic techniques. For example, in certain embodiments, acombined nano-imprint lithography can be used to achieve a desiredphysical surface structure, and a holographic exposure can be used toachieve a desired liquid crystal alignment. Other implementations arealso possible, and within embodiments of the present technology.

If orientated appropriately, an LCP based SRG can act like a waveretarder and rotate the polarization state of an incoming beam. Forexample, if the input-coupler 112 and the output-coupler 116 are bothLCP based SRGs, where the output-coupler 116 has grating lines that areorthogonal to the input-coupler 112, this should increase the opticalefficiency of the waveguide. Additionally, implementing theintermediate-component 114 as an LCP based SRG should also increase theoptical efficiency of the waveguide.

Where the input-coupler 112, the intermediate-component 114 and/or theoutput-coupler 116 is/are an LCP based SRG, each such LCP based SRG canbe formed on one of the major planar surfaces 108 or 110 of thebulk-substrate 106. It is also possible that at least one of theinput-coupler 112, the intermediate-component 114 or the output-coupler116 is an LCP based SRG formed on one of the major planar surfaces(e.g., 108) of the bulk-substrate 106, while at least one other one ofthe input-coupler 112, the intermediate-component 114 or theoutput-coupler 116 is an LCP based SRG formed on the other one of themajor planar surfaces (e.g., 110) of the bulk-substrate 106.

In embodiments where the waveguide 100 includes anintermediate-component 114 that is implemented as an LCP based SRG, thevarious light beams that are reflected and diffracted by the surfacerelief grating lines of the intermediate-components 114 will end uphaving a heterogeneous polarization distribution. This is beneficial inthat the heterogeneous polarization distribution compensates that theadverse effects of the multiple-loop interference that, if notcompensated for, would cause non-uniformities in local intensity.

Double-Sided Diffractive Optical Elements

As noted above, in the discussion of FIGS. 1A, 1B and 1C, in certainembodiments the input-coupler 112, the intermediate-component 114 andthe output-coupler 116 can all be implemented as SRGs. Such SRGs can allbe located in or on the same one of the major planar surfaces 108 or 110of the bulk-substrate 106 of the waveguide 100. Alternatively, it isalso possible that at least one of the input-coupler 112, theintermediate-component 114 or the output-coupler 116 is an SRG formed inor on one of the major planar surfaces (e.g., 108) of the bulk-substrate106, while at least one other one of the input-coupler 112, theintermediate-component 114 or the output-coupler 116 is an SRG formed inor on the other one of the major planar surfaces (e.g., 110) of thebulk-substrate 106.

In certain embodiments of the present technology, which will now bediscussed with reference to FIGS. 9A and 9B, any one, two or all of aninput-coupler, an intermediate-component or an output-coupler can beimplemented as a double-sided SRG, or more generally, as a double-sidedDOE. FIGS. 9A and 9B are, respectively, top and side views of awaveguide 900 wherein each the input-coupler, the intermediate-componentand the output-coupler are implemented as double-sided DOEs. The frontview of the waveguide 900 can look, e.g., the same as or similar to thefront view of the waveguide 100 shown in FIG. 1A. Such a front view ofthe waveguide 900 is not included, since the front view would not showhow the input-coupler, the intermediate-component and the output-couplerare implemented as double-sided DOEs, because DOEs on one of the planarmajor surfaces 108 or 110 of the bulk-substrate 106 would completelyoverlap the DOEs on the other one of the planar major surfaces.

Referring to FIGS. 9A and 9B, where the input-coupler is a double-sidedDOE, the input-coupler includes a DOE 112 a on the major planar surface110 as well as a DOE 112 b on the other major planar surface 108.Accordingly, such an input-coupler can be referenced as theinput-coupler 112 a-b. Where the intermediate-component is adouble-sided DOE, the intermediate-component includes a DOE 114 a on themajor planar surface 110 as well as a DOE 114 b on the other majorplanar surface 108, and thus, can be referenced as theintermediate-component 114 a-b. Similarly, where the output-coupler is adouble-sided DOE, the output-coupler includes a DOE 116 a on the majorplanar surface 110 as well as a DOE 116 b on the other major planarsurface 108, and thus, can be referenced as the output-coupler 116 a-b.The input-coupler 112 a-b, the intermediate-component 114 a-b and theoutput-coupler 116 a-b can be collectively referenced as double-sidedDOE components 112 a-b, 114 a-b and 116 a-b.

In accordance with certain embodiments, the grating period andorientation of each DOE, of a pair of DOEs associated with one of thecomponents 112 a-b, 114 a-b or 116 a-b, are precisely matched so as tonot adversely affect the modulation transfer function (MTF) of theimaging system and/or produce double imaging. For example, for thecomponent 112 a-b, the grating period and orientation of the DOE 112 aare precisely matched to (i.e., the same as) the grating period andorientation of the DOE 112 b. Similarly, for the component 114 a-b, thegrating period and orientation of the DOE 114 a are precisely matched tothe grating period and orientation of the DOE 114 b; and for thecomponent 116 a-b, the grating period and orientation of the DOE 116 aare precisely matched to the grating period and orientation of the DOE116 b.

In accordance with certain embodiments, included in an opposing pairDOEs, associated with one of the components 112 a-b and 116 a-b, is botha transmission grating and a reflective grating. For example, for thecomponent 112 a-b, the DOE 112 a can be a transmissive grating and theDOE 112 b can be reflective grating. For another example, for thecomponent 116 a-b, the DOE 116 a can be a reflective grating, and theDOE 116 b can be a transmissive grating. Other variations are alsopossible, and are within embodiments of the present technology. Wherethe intermediate-component is a double-sided DOE, both DOEs should bereflective gratings, because the intermediate-component is not intendedto couple light out of the waveguide. In other words, for the component114 a-b, the DOE 114 a and the DOE 114 b should both be reflectivegratings.

For a single-sided DOE waveguide, polarization and phase changes areonly introduced in light propagating through the bulk-substrate (e.g.,106) when they interact with the DOE. With the double-sided DOEorientation, where DOEs are included in or on both major planar sides108 and 110 of the bulk-substrate 106, twice the number of diffractiveinteractions are induced, wherein each interaction with a DOE inducesphase and polarization changes. More specifically, the use ofdouble-sided DOEs will increase the phase diversity of the wave frontsof light traveling within the waveguide, since light that is notdiffracted by a first DOE (of a pair) but is diffracted by a second DOE(of the pair) will have traveled a greater path length (having traveledthrough the thickness of the bulk-substrate 106) before being incidenton the second DOE (of the pair). Further, where every diffraction and/orreflection from a DOE causes a polarization rotation, the inclusion ofDOEs in or on both major planar sides 108 and 110 of the bulk-substrate106 will induce twice the number of polarization rotations, which willprovide for a heterogeneous polarization distribution. Accordingly, theinclusion of double-sided DOEs can be used to compensate formultiple-loop interference caused by the intermediate-component 114 (ifone is present), provide for a heterogeneous polarity distribution ofthe light that is incident on the output-coupler 116 (after havingtraveled through the waveguide 100), and provide for a substantiallyuniform pupil distribution, and thereby, such embodiments can be used toprovide a substantially uniform intensity distribution in the light thathas exited the waveguide 100 at the output-coupler 116.

Another one of the benefits of the double-side DOEs is that they shouldprovide for a better system efficiency compared to a single-sided DOEsystem, because at least a portion of any light that is not diffractedby the first one of the pair of DOEs, upon which the light is firstincident, will likely be diffracted by the second one of the pair ofDOEs.

The DOEs included in or on one of the major planar surfaces 108 or 110can be etched into one of the major planar surfaces 108 or 110 of thebulk-substrate 106, in which case each such DOE can be said to be formed“in” the bulk-substrate 106. Alternatively, each DOE (e.g., which can bean SRG) can be physically formed in a coating that covers one of themajor planar surfaces 108 or 110 of the bulk-substrate 106, in whichcase each such DOE can be said to be formed “on” the bulk-substrate 106.Such a coating can be isotropic, or alternatively, can be an LCP coatingthat is anisotropic, the benefits of which were discussed above. Forexample, for each double-sided DOE, one or both of the DOEs can be anLCP based SRG.

The DOEs formed in or on one of the major planar surface 108 or 110 canbe formed in the same, or in a different manner, than the DOEs formed inor on the other one of the major planar surfaces 108. Either way, thecomponents 112 a-b, 114 a-b and 116 a-b are considered parts of thewaveguide 900.

In certain embodiments, where the components 112 a, 114 a and 116 a areDOEs that are formed in a coating covering the major planar surface 110,and the components 112 b, 114 b and 116 b are DOEs that are formed in acoating covering the other major planar surface 108, the coatingscovering the opposing major planar surfaces 110 and 108 can be of thesame or different types of coating materials, and can be of the same ordifferent thicknesses.

Each of an input-coupler, an intermediate-component and anoutput-coupler of a waveguide can be implemented as a double-side DOE.Alternatively, one or more of an input-coupler, anintermediate-component or an output-coupler of a waveguide can beimplemented as a double-side DOE, while other one(s) of the componentsare not. It is also possible that one or more of an input-coupler or anoutput-coupler be implemented as a double-side DOE, and that thewaveguide not include an intermediate-component at all.

Switchable Liquid Crystal Layer

In accordance with certain embodiments of the present technology, awaveguide includes switchable liquid crystal (LC) layer that can be usedto improve the local non-uniformity for light exiting the waveguide atan output-coupler. In certain such embodiments, patterns in the LC layercan be selectively turned on or off at different points in the eye box,as discussed in further detail below. The switchable (LC) layer is anexample of a volume layer that can be embedded within a bulk-substrateto cause the light that is output from a waveguide by an output-couplerto have a more uniform intensity distribution compared to if the volumelayer were absent.

An example of such an embodiment will now be described with reference toFIG. 10, which is a top view of a waveguide 1000 that includes aswitchable liquid crystal (LC) layer 1020 embedded between major planarsurfaces 1010 and 1008 of the waveguide 1000. More specifically, theswitchable LC layer 1020 is sandwiched between a pair of bulk-substrates106 a and 106 b. Each of the bulk-substrates 106 a, 106 b can be made ofthe same bulk material and can have the same index of refraction.Alternatively, the bulk-substrates 106 a, 106 b can be made differentmaterials than one another and can have the different indices ofrefraction than one another, which can provide for the benefitsdiscussed above with reference to FIG. 8. For simplicity, unless statedotherwise, when discussing FIG. 10 it will be assumed that thebulk-substrates 106 a and 106 b are made of the same material and havethe same index of refraction. The thicknesses of the bulk-substrates 106a, 106 b can be the same as, or different than, one another. Forsimplicity, unless stated otherwise, it will be assumed that thethicknesses of the bulk-substrates 106 a and 106 b are the same.

In certain embodiments, transparent electrodes, the shapes and sizes ofwhich define the shapes and sizes of the liquid crystal pixels that canbe produced using the switchable LC layer 1020, can be patterned on bothsides of the switchable LC layer 1020, e.g., on or adjacent to the innersurfaces of the bulk-substrates 106 a and 106 b. Alternatively,transparent electrodes can be interdigitated electrodes that arepatterned on or adjacent to only one side of the switchable LC layer1020, e.g., on or adjacent the inner surface of only one of thebulk-substrates 106 a and 106 b. Such transparent electrodes can bemade, e.g., of indium tin oxide (ITO), but are not limited thereto. Incertain embodiments where the transparent interdigitated electrodes arepatterned on or adjacent to only one side of the switchable LC layer1020, the switchable LC layer can be a twisted nematic (TN) LC layerincluding an alignment component (e.g., an alignment sub-layer) toorient either the top or bottom of LC molecules.

Selectively application of an electric field, e.g., induced by applyinga voltage between pairs of electrodes (which can be opposing orinterdigitated) can be used to selectively turn on and off specificliquid crystal pixels, which can also be referred to more succinctly aspixels. Such electrodes can be controlled, e.g., by a controller 1030 ofthe system in which the waveguide 1000 is include, which as noted above,can be an imaging system such as an HMD, NED, or HUD system, but is notlimited thereto. Such a controller 1030 can be implemented by amicrocontroller, a microprocessor, or an application specific integratedcircuit (ASIC), or discrete circuitry, but is not limited thereto.

In accordance with specific embodiments of the present technology, theelectrodes could be individually addressed (i.e., individual turned onor off) to change the optical properties (e.g., the index of refraction)in the switchable LC layer 1020 and thereby change the opticalproperties of the waveguide at various different locations of an eyebox.

The LC layer 1020 can act as a reflective surface within the waveguide1000, wherever the index of refraction of the LC layer 1020 differs fromthat of the surrounding bulk-substrates 106 a and 106 b. For example,wherein light that is traveling through the bulk-substrate 106 a isincident on the boundary (between the bulk-substrates 106 a and the LClayer 1020), a portion of the light incident on the boundary (asdependent on the indexes of refraction of the two mediums meeting at theboundary, and the angle of incidence) can reflect back into thebulk-substrate 106 a through TIR, while another portion of the lightrefracts into the LC layer 1020, undergoes a certain degree ofretardation (i.e., polarization rotation) and enters the otherbulk-substrate 106 b to continue TIR in the waveguide 1000. Thisintroduction of retardation will change the polarization state of thelight passing through the waveguide and help overcome pupil replicationnon-uniformity issues, which were described above with reference to FIG.5A.

In certain embodiments, each of the liquid crystal pixels, which areindividually addressable by the controller 1030, can either be turnedoff or on, e.g., by applying either no voltage or a predeterminednon-zero voltage between pairs of electrodes associated with the pixel.In other embodiments, liquid crystal pixels can be tuned on to varyingdegrees, such that there are more states (i.e., three or more) thanmerely fully off or fully on. In such latter embodiments, individualpixels or groups of pixels can be calibrated by tuning the pixels to theright levels depending on their use. For example, a calibration can beperformed to optimize some measure of image quality, such as uniformityin intensity. Other variations are also possible, and within theembodiments of the present technology.

In the embodiments where the waveguide 1000 includes a switchable LClayer 1020, the size of the liquid crystal pixels should be large enoughsuch that the pixels, when turned on, do not act as a diffractiongrating. This should be ensured by making the pixel sizes, in both thehorizontal and vertical directions (i.e., in directions that areparallel to the major planar surfaces), at least one-thousand times(i.e., 1000×) the wavelength of the light for which the waveguide 1000is being used as an optical transmission medium. For example, for redlight having a wavelength of 620 nm, the size of the pixels should be atleast 630 μm. In certain embodiments, the pixels are each at least 1000μm (i.e., at least 1 mm) in both the horizontal and vertical directions,which should ensure that they do not operate as a diffraction grating,although minor edge or aperture diffractions may be unavoidable. Moregenerally, the size of each of substantially all (i.e., at least 90%) ofthe pixels, in both horizontal and vertical directions that are parallelto the first and second major planar surfaces of the bulk-substrate ofplanar optical waveguide, is least one-thousand times the wavelength ofthe light for which the waveguide is being used as an opticaltransmission medium.

Electrodes that define pixels can be patterned to coincide with any one,two or all of the input-coupler 112, the intermediate-component 114 orthe output-coupler 116. The shapes and patterns of the electrodes can bethe same for each of the components 112, 114 and 116, or can bedifferent for separate ones of the components 112, 114 and 116.

In embodiments, such as the ones described with reference to FIG. 10,where there are two bulk-substrates (e.g., 106 a and 106 b) with anotheroptical component (e.g., the switchable LC layer 1020) embeddedtherebetween, the two bulk-substrates (e.g., 106 a and 106 b) can becollectively referred to as a bulk-substrate having an embedded opticalcomponent embedded therein, or more specifically, embedded between themajor planar surfaces of the bulk-substrate. In accordance with certainembodiments, liquid crystal pixels can be temporally adjusted (e.g.,dithered) to provide for different optical path lengths across variouspixels over time. The temporally adjusted (e.g., dithered) liquid pixelscan be used to provide increased optical path length diversity,increased phase diversity, and increased polarization diversity, tothereby provide additional improvements in the uniform intensitydistribution. In such embodiments, the switching speeds may be on theorder of about 2 to 4 microseconds, in which case the LC layer 1020should include fast switching liquid crystals.

In certain embodiments, where the system that includes the waveguide1000 also includes an eye tracking subsystem that provides eye trackingcapabilities, certain liquid crystal pixels can be turned on or off(totally, or to varying degrees) in dependence on gaze positions and/orgaze angles as determined using the eye tracking subsystem. For example,a calibration can be performed to determine which pixels to turn on (andto what extent the pixels should be turned on) to optimize some measureof image quality (such as uniformity in intensity) for various differentgaze positions and/or gaze angles. For a more specific example,information can be stored in a table or other manners within thecontroller 1030, or a data store (e.g., memory) associated therewith,that specifies which pixels to turn on (and to what extent the pixelsshould be turned on) in dependence on different gaze positions and/orgaze angles. The eye tracking subsystem can provide, to the controller1030, gaze positions and/or gaze angles in real-time, thereby enablingthe controller 1030 to determine, in real-time, which pixels to turn on(and to what extent the pixels should be turned on) and off. Othervariations are also possible, and with the scope of embodimentsdescribed herein.

Hybrid SRG-VBG Gratings

In accordance with certain embodiments of the present technology, awaveguide includes one or more hybrid gratings can be used to providefor substantially uniform local and global intensity distributions inlight exiting the waveguide at an output-coupler. More specifically,such a hybrid grating can include by an SRG and a volume Bragg grating(VBG), and thus, can be referred to as a hybrid SRG-VBG grating. A VBGis a transparent grating with a periodic variation of the refractiveindex, so that a high diffraction efficiency may be reached in somewavelength range (bandwidth) around a certain wavelength which fulfillswhat is known as the Bragg condition. The VBG(s) can be included in oras a volume layer that can be embedded within a bulk-substrate to causethe light that is output from a waveguide by an output-coupler to have amore uniform intensity distribution compared to if the volume layer wereabsent.

An example of such an embodiment will now be described with reference toFIG. 11, which is a top view of a waveguide 1100 that includes a VBGlayer 1120 embedded between major planar surfaces 1110 and 1108 of thewaveguide 1100. More specifically, the VBG layer 1020 is sandwichedbetween a pair of bulk-substrates 106 a and 106 b. Each of thebulk-substrates 106 a, 106 b can be made of the same bulk material andcan have the same index of refraction. Alternatively, thebulk-substrates 106 a, 106 b can be made different materials than oneanother and can have the different indexes of refraction than oneanother, which can provide for the benefits discussed above withreference to FIG. 8. For simplicity, unless stated otherwise, whendiscussing FIG. 11 it will be assumed that the bulk-substrates 106 a and106 b are made of the same material and have the same index ofrefraction. The thicknesses of the bulk-substrates 106 a, 106 b can bethe same as, or different than, one another. For simplicity, unlessstated otherwise, it will be assumed that the thicknesses of thebulk-substrates 106 a and 106 b are the same.

In certain embodiments, such as the ones described with reference toFIG. 11, where there are two bulk-substrates (e.g., 106 a and 106 b)with other optical components (e.g., VBGs) embedded therebetween, thetwo bulk-substrates (e.g., 106 a and 106 b) can be collectively referredto as a bulk-substrate having an embedded optical component embeddedtherein, or more specifically, embedded between the major planarsurfaces of the bulk-substrate.

In certain embodiments, in which the waveguide 1100 includes a VBG layer1120 embedded between the major planar surfaces 1110 and 1108 of thewaveguide 1100, each of the components 112, 114 and 116 is implementedas an SRG. In such embodiments, various different VBGs can be formedwithin the VBG layer 1020, such that a separate VBG corresponds to anyone, two or all of the input-coupler 112, the intermediate-component 114and/or the output-coupler 116. For example, a first VBG 1122 can becongruent with and completely overlap with the input-coupler 112, asecond VBG 1124 can be congruent with and completely overlap with theintermediate-component 114, and a third VBG 1126 can be congruent withand completely overlap with the output-coupler 116. Where this is thecase, the input-coupler 112 and the first VBG 1122 can be collectivelyreferred to as an SRG-VBG hybrid input-grating, theintermediate-component 114 and the second VBG 1124 can be collectivelyreferred to as an SRG-VBG hybrid intermediate-grating, and theoutput-coupler 116 and the third VBG 1126 can be collectively referredto as an SRG-VBG hybrid output-grating. More generally, such pairs canbe referred to as SRG-VBG hybrid gratings. In such embodiments, thefirst, second and third VBGs 1122, 1124 and 1126 can also be referred,respectively, as an input-VBG 1122, an intermediate-VBG 1124 and anoutput-VBG 1126.

In accordance with certain embodiments, the grating period andorientation of the SRG and the corresponding VBG, of an SRG-VBG hybridgrating, are precisely matched to one another so as to not adverselyaffect the modulation transfer function (MTF) of the imaging systemand/or produce double imaging. For example, for the SRG-VBG hybridinput-grating, the grating period and orientation of the input-VBG 1122are precisely matched to (i.e., the same as) the grating period andorientation of the SRG input-coupler 112. Similarly for the SRG-VBGhybrid intermediate-grating, the grating period and orientation of theintermediate-VBG 1124 are precisely matched to the grating period andorientation of the SRG intermediate-component 114; and for the SRG-VBGhybrid output-grating, the grating period and orientation of theoutput-VBG 1126 are precisely matched to the grating period andorientation of the SRG output-coupler 116.

For any individual SRG-VBG hybrid grating, the SRG and the VBG can bothbe transmissive gratings, can both be reflective gratings, or one can bea transmissive grating while the other is a transmissive grating.

Each VBG can be a diffractive device formed by recording a volume phasegrating, or hologram, in a polymer dispersed liquid crystal (PDLC)mixture. Referring to FIG. 11, each VBG can be fabricated, e.g., byfirst placing a mixture of photopolymerizable monomers and liquidcrystal material between opposing parallel inner planar surfaces of thebulk-substrates 106 a and 106 b. A VBG can then be recorded byilluminating the liquid material with two mutually coherent laser beams,which interfere to form the desired grating structure. During therecording process, the monomers polymerize and the PDLC mixtureundergoes a phase separation, creating regions densely populated byliquid crystal micro-droplets, interspersed with regions of clearpolymer. The alternating liquid crystal-rich and liquid crystal-depletedregions form the fringe planes of the grating. The resulting VBG canexhibit very high diffraction efficiency.

In certain embodiments the VBGs can be switchable Bragg gratings (SBGs),in which case one or both of the inner planar surfaces of thebulk-substrates 106 a and 106 b can support transparent electrodes forapplying an electric field across the PDLC layer. In such embodiments,when an electric field is applied to the SBG via transparent electrodes,the natural orientation of the LC droplets is changed causing therefractive index modulation of the fringes to reduce and the hologramdiffraction efficiency to drop to very low levels. Note that thediffraction efficiency of the device can be adjusted, by means of theapplied electric field (e.g., a voltage), over a continuous range fromnear 100% efficiency with no voltage applied to essentially zeroefficiency with a sufficiently high voltage applied. Such electrodes canbe controlled, e.g., by a controller 1130 of the system in which thewaveguide 1100 is include, which as noted above, can be an imagingsystem such as an HMD, NED, or HUD system, but is not limited thereto.Such a controller 1130 can be implemented by a microcontroller, amicroprocessor, or an application specific integrated circuit (ASIC), ordiscrete circuitry, but is not limited thereto. The controller 1130 neednot be included where the VBGs are not switchable.

As noted above, the bulk-substrates 106 a, 106 b, between which the VBGsare embedded, can have the same indexes of refraction, or alternatively,can be made different materials than one another and can have thedifferent indexes of refraction than one another. This latter case wouldessentially combine the SRG-VBG hybrid grating embodiments, describedwith reference to FIG. 11, with the mismatched index of refractionembodiments described above with reference to FIG. 8.

If the components 112, 114 and 116 were each implemented as only an SRG,then polarization and phase changes are only introduced in lightpropagating through the bulk-substrate when the light interacts with theSRG. With the SRG-VBG hybrid gratings, twice the number of diffractiveinteractions are induced, wherein each interaction with a gratinginduces phase and polarization changes, thereby homogenizing the outputdistribution.

More specifically, the use of SRG-VBG hybrid gratings will increase thephase diversity of the wave fronts of light traveling within thewaveguide, since light that is not diffracted by an SRG (of a hybridgrating) but is diffracted by a VBG (of the hybrid grating), or viceversa, will have traveled a greater path length (e.g., for havingtraveled through the thickness of the bulk-substrate 106 a) before beingincident on the VBG. Further, where every diffraction and/or reflectionfrom a grating causes a phase rotation, the inclusion of both SRGs andVBGs will induce twice the number of polarization rotations, which willprovide for a heterogeneous polarization distribution. Accordingly, theinclusion of SRG-VBG hybrid gratings can be used to compensate formultiple-loop interference caused by the intermediate-component 114 (ifone is present), provide for a heterogeneous polarity distribution ofthe light that is incident on the output-coupler 116 (after havingtraveled through the waveguide 100), and provide for a substantiallyuniform pupil distribution, and thereby, such embodiments can be used toprovide a substantially uniform intensity distribution in the light thathas exited the waveguide 100 at the output-coupler 116.

Another one of the benefits of the SRG-VBG hybrid gratings is that theyshould provide for a better diffractive efficiency compared to SRGsalone, because at least a portion of any light that is not diffracted bythe an SRG, upon which the light is first incident, will likely bediffracted by the corresponding VBG, or vice versa.

Another advantage of using VBGs is that the angular bandwidth can behighly tuned to a set of input angles, to further improve that intensityuniformity, e.g., by tuning the VBGs to angles that are not diffractedefficiently by the corresponding SRG.

K-vectors of a diffraction grating, such as a VGB, are, by definition,normal to (i.e., perpendicular to) the fringe planes of the diffractiongrating. The term k-vector angle, as used herein, refers to the angle ofa k-vector relative to the surface normal of the diffraction grating. Inother words, while each k-vector is perpendicular to a respective fringeplane, each k-vector can have a different k-vector angle relative to thesurface normal of the diffraction grating. In accordance with certainembodiments, the input-VBG 1122 of has a rolled k-vector, whichgradually varies between boundaries of the input-VBG 1122, in order toimprove the diffraction efficiency of the input-VBG 1122. For example,referring to FIG. 12, shown therein are two exemplary fringe planes 1202of numerous fringe planes, the others of which are not shown. Suchfringe planes 1202, which can also referred to as fringes, gratingplanes or Bragg planes, define a grating periodicity (A). Also shown inFIG. 12 are dashed lines 1204 which are normal to the surface of thediffraction grating. Two k-vectors are also shown, each of which isperpendicular to a respective fringe plane 1202, and each of which has adifferent k-vector angle relative to the surface normal of thediffraction grating. Alternatively, the k-vectors could include two ormore distinct k-vectors for different parts of the input-VBG 1122, whichare used to optimize an angular bandwidth to the center of the field ofview of the display. In this embodiment, it would be advantageous forthe input-VBG to have two distinct k-vectors that improve thediffraction efficiency at the extremes of the field of view of thedisplay to improve the global non-uniformity of the system.

It should be understood that a Switchable Volume Bragg Grating can bepixelated and switched on partially so as to optimize the diffractionefficiency across the grating surface. This can be used in-conjunctionwith an eye tracker to optimize the diffraction efficiency profile for aparticular eye location. In addition, if the SBG is fast enough, it canbe temporally dithered to improve the luminance uniformity over a pixelswitching time.

Various embodiments of the present technology, which were describedabove, can be utilized in various different combinations. For example,an LCP coating 106 can be added to a waveguide that includes one or moreSRG-VBG hybrid gratings. For another example, as was already describedabove, a waveguide that includes one or more SRG-VBG hybrid gratings canalso include an adjacent planar optical-component that has a mismatchedindex of refraction relative to a bulk-substrate on or in which SRGs areprovided. For a further example, a waveguide can include LCP basedSRG(s) in or on one of its major planar surfaces, and can include an LCPcoating (without grating included therein) on its other major planarsurface. For still another example, where a waveguide includes one ormore SRG-VBG hybrid gratings, the SRG(s), of one or more of the hybridgratings, can be LCP based SRG(s). These are just a few exemplary waysin which embodiments of the present technology described herein can becombined, which is not intended to be all encompassing.

Certain embodiments described herein relate to an apparatus for use inreplicating an image associated with an input-pupil to an output-pupil.Such an apparatus can include a planar optical waveguide including abulk-substrate, and also including an input-coupler, anintermediate-component and an output-coupler any one of which is eitherformed in, on or embedded within the bulk-substrate. In certainembodiments, the input-coupler is configured to couple lightcorresponding to the image associated with the input-pupil into thebulk-substrate of the waveguide and towards the intermediate-component,the intermediate-component is configured to perform one of horizontal orvertical pupil expansion and to direct the light corresponding to theimage towards the output-coupler, and the output-coupler is configuredto perform the other one of horizontal or vertical pupil expansion andto couple the light corresponding to the image, which travels in theplanar optical waveguide from the input-coupler to the output-coupler,out of the waveguide so that the light is output and imaged from theoutput-pupil. The bulk-substrate can include a first major planarsurface and a second major planar surface opposite and parallel to thefirst major planar surface. In certain embodiments theintermediate-component is not included.

In certain embodiments an adjacent planar optical component is adjacentto one of the first and second major planar surfaces of thebulk-substrate and is configured to cause the light that is output fromthe waveguide by the output-coupler to have a more uniform intensitydistribution compared to if the adjacent planar optical component wereabsent. In certain embodiments the adjacent planar optical componentcomprises at least one of a liquid crystal polymer (LCP) coating orsubstrate, or a coating or substrate that has an index of refractionthat is different than an index of refraction of the bulk-substrate.

In certain embodiments, a portion of the light traveling from theinput-coupler to the output-coupler travels by way of TIR only withinthe bulk-substrate, and a further portion of the light traveling fromthe input-coupler to the output-coupler travels through both thebulk-substrate and through the adjacent planar optical component. Theadjacent planar optical component can be configured to mitigate adverseeffects of multiple-loop interference that would be caused by theintermediate-component if the adjacent planar optical component wereabsent. The adjacent planar optical component can also be configured torandomize polarizations of the light traveling within the waveguide. Forexample, the adjacent planar optical component can be configured torandomize polarizations of the light traveling within the waveguide sothat light traveling within the waveguide that is incident on theoutput-coupler has a substantially heterogeneous polarizationdistribution. In certain embodiments, the adjacent planar opticalcomponent is configured to offset phases of wave fronts of lighttraveling within the waveguide so that wave fronts of light that areoutput from the waveguide by the output-coupler have a substantiallyheterogeneous phase distribution. In certain embodiments, the adjacentplanar optical component is configured provide a substantially uniformpupil distribution in the light traveling within the waveguide that isincident on the output-coupler.

The adjacent planar optical component can be isotropic. Alternatively,the adjacent planar optical component can be anisotropic. In certainembodiments, the adjacent planar optical component is birefringent. Incertain embodiments, the adjacent planar optical component comprises anLCP coating. In specific embodiments, the adjacent planar opticalcomponent comprises a further bulk-substrate, wherein the index ofrefraction of the adjacent planar optical component is different thanthe index of refraction of the bulk-substrate. In certain embodiments,the intermediate-component is not present.

In accordance with certain embodiments, one or more of theinput-coupler, the intermediate-component or the output-couplercomprises a surface relief grating (SRG) that is formed in a liquidcrystal polymer (LCP) coating. In some embodiments, the LCP coating, inwhich the one or more of the input-coupler, the intermediate-componentor the output-coupler is formed as an SRG, can cover one of the majorplanar surfaces of the bulk-substrate. The one or more of theinput-coupler, the intermediate-component or the output-coupler that isformed as an SRG in the LCP coating can be configured to rotate apolarization of light that is incident thereon. In certain embodiments,each one of the input-coupler, the intermediate-component and theoutput-coupler is formed as an SRG in the LCP coating. Where theintermediate-component comprises an SRG that is formed in an LCPcoating, this should mitigate adverse effects of multiple-loopinterference that would be caused by the intermediate-component if theintermediate-component were an SRG formed in or on an isotropicmaterial.

In accordance with certain embodiments, one or more of theinput-coupler, the intermediate-component or the output-couplercomprises a double-sided diffractive optical element (DOE). In suchembodiments, each double-sided DOE can comprise a first grating, whichis formed in or on a first major planar surface of a bulk-substrate ofthe waveguide, and a corresponding second grating that is formed in oron a second major planar surface of the bulk-substrate. In accordancewith certain embodiments, for each double-sided DOE, the grating periodand orientation of the first and second gratings of the double-sidedDOE, which are formed respectively in or on the first and second majorplanar surfaces of the bulk-substrate, are matched to one another. Incertain embodiments, for each double-sided DOE, at least one of thefirst and second gratings of the double-sided DOE comprises a surfacerelief gratings (SRG). In certain embodiments, for at least onedouble-sided DOE, one of the first and second gratings comprises atransmissive grating, and the other comprises a reflective grating. Incertain embodiments, the intermediate-component comprises a double-sidedDOE, wherein the first and second gratings of the intermediate-componentcomprise reflective gratings. In certain embodiment, theintermediate-component is not present.

In accordance with certain embodiments, a switchable liquid crystal (LC)layer is embedded between the first and second major planar surfaces ofthe bulk-substrate of the waveguide, wherein the switchable LC layer isconfigured to cause light that is output by the output-coupler to have amore uniform intensity distribution compared to if the switchable LClayer were absent. In certain embodiments, the switchable LC layer isdistinct from, and does not provide a function of any one of, aninput-coupler, an intermediate-component and an output-coupler. Theswitchable LC layer can include first and second major planar sides,wherein at least one of the sides includes transparent electrodespatterned thereon that specify sizes of pixel that are formed when anelectric field is applied between pairs of the transparent electrodes.In certain embodiments, a size of each of substantially all of thepixels, in both horizontal and vertical directions that are parallel tothe first and second major planar surfaces of the bulk-substrate ofplanar optical waveguide, is least one-thousand times the wavelength ofthe light for which the waveguide is being used as an opticaltransmission medium. In certain embodiments, a size of each ofsubstantially all of the pixels, in both horizontal and verticaldirections that are parallel to the first and second major planarsurfaces of the bulk-substrate of planar optical waveguide, is least 1mm. In certain embodiments, the pixels are configured to not operate asa diffraction grating. An apparatus can also include a controller thatis configured to selectively turn on and off individual pixels. Incertain embodiments, a controller can be configured to selectivelyaddress individual pixels and selectively apply one of three or moredifferent voltages between pairs of electrodes associated withindividual pixels. The LC layer can be configured to mitigate adverseeffects of multiple-loop interference that would be caused by theintermediate-component if the LC layer were absent.

In certain embodiments, one or more of the input-coupler, theintermediate-component or the output-coupler comprises a hybrid SRG-VBGgrating that includes a surface relief grating (SRG) and correspondingvolume Bragg grating (VBG). Each hybrid SRG-VBG grating can comprise anSRG that is formed in or on one of the first and second major planarsurface of the bulk-substrate and a corresponding congruent andcompletely overlapping VBG that is embedded between the first and secondmajor planar surface of the bulk-substrate. In certain embodiments, foreach hybrid SRG-VBG grating, the grating period and orientation of theSRG and the corresponding VBG are matched to one another. In certainembodiments, for each individual hybrid SRG-VBG grating, the SRG and thecorresponding VBG are either both transmissive gratings or bothreflective gratings. In certain embodiments, for at least one hybridSRG-VBG grating, the VBG comprises a switchable Bragg grating (SBG).Where the intermediate-component comprises a hybrid SRG-VBG grating,this should mitigate adverse effects of multiple-loop interference thatwould be caused by the intermediate-component if theintermediate-component only comprised an SRG.

Certain embodiments of the present technology relate to methods for usewith a planar optical waveguide including a bulk-substrate having a pairof opposing major planar surfaces, and the waveguide also including aninput-coupler, an intermediate-component and an output-coupler any oneof which is either formed in, on or embedded within the bulk-substrate.Such a method can include

producing an image, using the input-coupler to couple lightcorresponding to the image into the bulk-substrate of the waveguide andtowards the intermediate-component, using the intermediate-component toperform one of horizontal or vertical pupil expansion and to direct thelight corresponding to the image towards the output-coupler, and usingthe output-coupler to perform the other one of horizontal or verticalpupil expansion and to couple the light corresponding to the image,which travels in the planar optical waveguide from the input-coupler tothe output-coupler, out of the waveguide. Such methods can also be usedwhere the intermediate-component is not present.

A method can include using an adjacent planar optical component,adjacent to one of the first and second major planar surfaces of thebulk-substrate of the waveguide, to cause the light that is output fromthe waveguide by the output-coupler to have a more uniform intensitydistribution compared to if the adjacent planar optical component wereabsent. In certain embodiments, the adjacent planar optical componentcomprises at least one of a liquid crystal polymer (LCP) coating orsubstrate, or a coating or substrate that has an index of refractionthat is different than an index of refraction of the bulk-substrate.Uses of the adjacent planar optical component were summarized above, andthus, need not be repeated.

A method can include using one or more surface relief grating (SRG) thatis formed in a liquid crystal polymer (LCP) coating to cause light thatis output from the waveguide by the output-coupler to have a moreuniform intensity distribution compared to if the adjacent planaroptical component were absent.

A method can include using one or more double-sided diffractive opticalelement (DOE) to cause light that is output from the waveguide by theoutput-coupler to have a more uniform intensity distribution compared toif the double-sided DOE(s) were absent.

A method can include using a switchable liquid crystal (LC) layerembedded between the first and second major planar surfaces of thebulk-substrate of the waveguide to cause light that is output by theoutput-coupler to have a more uniform intensity distribution compared toif the switchable LC layer were absent.

A method can include using one or more hybrid SRG-VBG grating to causelight that is output from the waveguide by the output-coupler to have amore uniform intensity distribution compared to if the hybrid SRG-VBGgrating(s) were absent.

Certain embodiments of the present technology relate to see-through,mixed reality display device systems. Such a system can include adisplay engine and a planar optical waveguide. The display engine isconfigured to produce an image. The planar optical waveguide can includea bulk-substrate, and can also include an input-coupler, anintermediate-component and an output-coupler any one of which is eitherformed in, on or embedded within the bulk-substrate. The input-coupleris configured to couple light corresponding to the image into thebulk-substrate of the waveguide and towards the intermediate-component.The intermediate-component is configured to perform one of horizontal orvertical pupil expansion and to direct the light corresponding to theimage towards the output-coupler. The output-coupler is configured toperform the other one of horizontal or vertical pupil expansion and tocouple the light corresponding to the image, which travels in the planaroptical waveguide from the input-coupler to the output-coupler, out ofthe waveguide. In certain embodiments the intermediate-component is notincluded. Further exemplary details of the input-coupler,intermediate-component and the output-coupler were provided above, andthus need not be repeated.

In such systems, any one or more of the various techniques for causingthe light that is output from the waveguide by the output-coupler tohave a more uniform intensity distribution can be used. For example, incertain embodiments the adjacent planar optical component comprises atleast one of a liquid crystal polymer (LCP) coating or substrate, or acoating or substrate that has an index of refraction that is differentthan an index of refraction of the bulk-substrate. As noted above, suchan adjacent planar optical component can be configured to mitigateadverse effects of multiple-loop interference that would be caused bythe intermediate-component if the adjacent planar optical component wereabsent, to randomize polarizations of the light traveling within thewaveguide, to offset phases of wave fronts of light traveling within thewaveguide so that wave fronts of light that are output from thewaveguide by the output-coupler have a substantially heterogeneous phasedistribution and/or to provide a substantially uniform pupildistribution in the light traveling within the waveguide that isincident on the output-coupler. In certain embodiments, one or more ofthe input-coupler, the intermediate-component or the output-couplercomprises a double-sided diffractive optical element (DOE). In certainembodiments, one or more of the input-coupler, theintermediate-component or the output-coupler comprises a surface reliefgrating (SRG) that is formed in a liquid crystal polymer (LCP) coating.In certain embodiments, a switchable liquid crystal (LC) layer isembedded between the major planar surfaces of the bulk-substrate of thewaveguide to cause light that is output by the output-coupler to have amore uniform intensity distribution compared to if the switchable LClayer were absent. In certain embodiments, one or more of theinput-coupler, the intermediate-component or the output-couplercomprises a hybrid SRG-VBG grating to cause light that is output fromthe waveguide by the output-coupler to have a more uniform intensitydistribution compared to if the hybrid SRG-VBG grating(s) were absent.In certain embodiments, a volume layer is embedded between the majorplanar surfaces of the bulk-substrate, wherein the volume layerconfigured to cause light that is output by the output-coupler to have amore uniform intensity distribution compared to if the volume layer wereabsent. The volume layer can include a separate volume Bragg grating(VBG) corresponding to each of the input-coupler, theintermediate-coupler and the output-coupler. Each of the VBGs cancomprise a switchable Bragg grating (SBG). In certain embodiments, thevolume layer includes a switchable liquid crystal layer that is distinctfrom, and does not provide a function of any one of, an input-coupler,an intermediate-component or an output-coupler. Additional details ofthe various embodiments are provided above, and thus need not berepeated.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. An apparatus for use in replicating an imageassociated with an input-pupil to an output-pupil, the apparatuscomprising: a planar optical waveguide including a bulk-substrate, andalso including an input-coupler, an intermediate-component and anoutput-coupler; the input-coupler configured to couple lightcorresponding to the image associated with the input-pupil into thebulk-substrate of the waveguide and towards the intermediate-component;the intermediate-component configured to perform one of horizontal orvertical pupil expansion and to direct the light corresponding to theimage towards the output-coupler; the output-coupler configured toperform the other one of horizontal or vertical pupil expansion and tocouple the light corresponding to the image, which travels in the planaroptical waveguide from the input-coupler to the output-coupler, out ofthe waveguide so that the light is output and imaged from theoutput-pupil; the bulk-substrate including a first major planar surfaceand a second major planar surface opposite and parallel to the firstmajor planar surface; and a switchable liquid crystal (LC) layer,embedded between the first and second major planar surfaces, configuredto cause light that is output by the output-coupler to have a moreuniform intensity distribution compared to if the switchable LC layerwere absent.
 2. The apparatus of claim 1, wherein the switchable LClayer is distinct from, and does not provide a function of any one of,an input-coupler, an intermediate-component and an output-coupler. 3.The apparatus of claim 1, wherein the switchable LC layer includes firstand second major planar sides at least one of which includes transparentelectrodes patterned thereon that specify sizes of pixel that are formedwhen an electric field is applied between pairs of the transparentelectrodes.
 4. The apparatus of claim 3, wherein a size of each ofsubstantially all of the pixels, in both horizontal and verticaldirections that are parallel to the first and second major planarsurfaces of the bulk-substrate of planar optical waveguide, is leastone-thousand times the wavelength of the light for which the waveguideis being used as an optical transmission medium.
 5. The apparatus ofclaim 3, wherein a size of each of substantially all of the pixels, inboth horizontal and vertical directions that are parallel to the firstand second major planar surfaces of the bulk-substrate of planar opticalwaveguide, is least 1 mm.
 6. The apparatus of claim 3, the pixels areconfigured to not operate as a diffraction grating.
 7. The apparatus ofclaim 1, further comprising a controller that is configured toselectively turn on and off individual pixels.
 8. The apparatus of claim1, further comprising a controller that is configured to selectivelyaddress individual pixels and selectively apply one of three or moredifferent voltages between pairs of electrodes associated withindividual pixels.
 9. The apparatus of claim 1, wherein the LC layer isconfigured to mitigate adverse effects of multiple-loop interferencethat would be caused by the intermediate-component if the LC layer wereabsent.
 10. An apparatus for use in replicating an image associated withan input-pupil to an output-pupil, the apparatus comprising: a planaroptical waveguide including a bulk-substrate, and also including aninput-coupler, an intermediate-component and an output-coupler; theinput-coupler configured to couple light corresponding to the imageassociated with the input-pupil into the bulk-substrate of the waveguideand towards the intermediate-component; the intermediate-componentconfigured to perform one of horizontal or vertical pupil expansion andto direct the light corresponding to the image towards theoutput-coupler; the output-coupler configured to perform the other oneof horizontal or vertical pupil expansion and to couple the lightcorresponding to the image, which travels in the planar opticalwaveguide from the input-coupler to the output-coupler, out of thewaveguide so that the light is output and imaged from the output-pupil;the bulk-substrate including a first major planar surface and a secondmajor planar surface opposite and parallel to the first major planarsurface; wherein one or more of the input-coupler, theintermediate-component or the output-coupler comprises a hybrid SRG-VBGgrating that includes a surface relief grating (SRG) and correspondingvolume Bragg grating (VBG).
 11. The apparatus of claim 10, wherein: thebulk-substrate includes a first major planar surface and a second majorplanar surface opposite and parallel to the first major planar surface;and each said hybrid SRG-VBG grating comprises an SRG that is formed inor on one of the first and second major planar surface of thebulk-substrate and a corresponding congruent and completely overlappingVBG that is embedded between the first and second major planar surfaceof the bulk-substrate.
 12. The apparatus of claim 10, wherein for eachsaid hybrid SRG-VBG grating, the grating period and orientation of theSRG and the corresponding VBG are matched to one another.
 13. Theapparatus of claim 10, wherein for each individual said hybrid SRG-VBGgrating, the SRG and the corresponding VBG are either both transmissivegratings or both reflective gratings.
 14. The apparatus of claim 10,wherein for at least one said hybrid SRG-VBG grating, one of the SRG andthe corresponding VBG is a transmissive grating and the other is areflective grating.
 15. The apparatus of claim 10, wherein for at leastone said hybrid SRG-VBG grating, the VBG comprises a switchable Bragggrating (SBG).
 16. The apparatus of claim 10, wherein theintermediate-component comprises a said hybrid SRG-VBG grating that isconfigured to mitigate adverse effects of multiple-loop interferencethat would be caused by the intermediate-component if theintermediate-component only comprised an SRG.
 17. A see-through, mixedreality display device system, comprising: a display engine configuredto produce an image; and a planar optical waveguide including abulk-substrate, and also including an input-coupler, anintermediate-component and an output-coupler; the input-coupler, theintermediate-component and the output-coupler comprising surface reliefgratings (SRGs); the input-coupler configured to couple lightcorresponding to the image into the bulk-substrate of the waveguide andtowards the intermediate-component; the intermediate-componentconfigured to perform one of horizontal or vertical pupil expansion andto direct the light corresponding to the image towards theoutput-coupler; the output-coupler configured to perform the other oneof horizontal or vertical pupil expansion and to couple the lightcorresponding to the image, which travels in the planar opticalwaveguide from the input-coupler to the output-coupler, out of thewaveguide; the bulk-substrate includes a first major planar surface anda second major planar surface opposite and parallel to the first majorplanar surface; and further comprising a volume layer embedded betweenthe first and second major planar surfaces of the bulk-substrate, thevolume layer configured to cause light that is output by theoutput-coupler to have a more uniform intensity distribution compared toif the volume layer were absent.
 18. The system of claim 17, wherein thevolume layer includes a separate volume Bragg grating (VBG)corresponding to each of the input-coupler, the intermediate-coupler andthe output-coupler.
 19. The system of claim 17, wherein each of the VBGscomprises a switchable Bragg grating (SBG).
 20. The system of claim 17,wherein the volume layer includes a switchable liquid crystal layer thatis distinct from, and does not provide a function of any one of, aninput-coupler, an intermediate-component or an output-coupler.